Terrestrial Arthropod Diversity in the United Arab Emirates

Abstract

Despite harsh climatic conditions and low and erratic rainfall patterns, the United Arab Emirates’ (UAE) terrestrial arthropod fauna is diverse and extremely well adapted to the local environment, with some species occurring in high abundance. Until recently, the UAE’s terrestrial arthropods were poorly studied. The past two decades have seen the knowledge of arthropod diversity increase dramatically, with more than 4000 species now known to occur in the Emirates, including hundreds of species that were previously unknown for the UAE and had never been recorded globally. With so many species recently added to the inventory of the nation, their ecology (i.e., life cycles, interactions, habitat needs) are yet to be studied. This presents a challenge for conservation planning, but also offers many opportunities for further study of these organisms. Where the life-histories of species are known, they demonstrate that arthropods of the UAE are an integral part of local food webs and contribute essential ecosystem services. As is the case globally, the UAE’s arthropods are under threat from habitat loss and destruction. The lack of long-term monitoring programs means that it is currently not possible to assess whether the trend of arthropod biodiversity loss seen worldwide is echoed in the UAE.

1 Introduction

Arthropods belong to the group of animals that don’t have a backbone, otherwise known as invertebrates. The lack of a backbone means that there is no internal skeleton to support their tissues, which is why arthropods have an outer shell known as an exoskeleton. The outer shell can be hard, as with some beetles, but in other cases it is soft, as in springtails. Arthropods also have jointed, or articulated, legs. The modern Latin word ‘Arthropoda’ has its origins in Greek, combining the word ‘arthron’, meaning ‘joint’, with the word ‘pous’ meaning ‘foot’. This phylum includes invertebrates such as insects, spiders, camel spiders, scorpions, millipedes, centipedes, and in the sea, organisms such as crabs, shrimps, lobsters, crayfish and many others. Arthropods are found everywhere, from the highest mountains to deserts (whether hot or cold), as well as in the deepest canyons of the seabed. This chapter focuses on the terrestrial arthropods of the United Arab Emirates (UAE). As it is not intended to provide a taxonomic account, arthropods are described in terms of functional groups or their ecological roles. Examples of specific arthropods belonging to two main terrestrial ecosystems found in the UAE, namely, mountains and wadis, and sand dunes or sand seas, are discussed.

2 The Emirates in a Global Context

To date, 1,163,161 arthropods have been described worldwide (Catalog of Life, June 2023) with the total number of arthropods—including those yet to be identified—estimated to be between twice to many times that number, constituting this phylum as having the highest biodiversity across the globe. Within the arthropod phylum, the Class known as insects (Insecta) is the most species diverse, representing 84% of all arthropods described and named to date. The class is further subdivided into taxonomic groups (Orders),containing such fauna as beetles (Coleoptera), earwigs (Dermaptera), butterflies and moths (Lepidoptera), flies (Diptera), termites (Isoptera), and barklice (Psocoptera), to name a few.

With arthropods being the most diverse group of animals worldwide, it is not surprising that it is also the animal group with the most species recorded in the Emirates. Of the currently recognized insect orders in existence worldwide today, two-thirds occur in the UAE. As is the case globally, the orders with the most insect species described in the UAE to date are the beetles, flies, butterflies and moths, as well as the order that encompasses the bees, wasps, ants and sawflies (Hymenoptera). Other arthropod orders represented in the UAE include spiders (Araneae), scorpions (Scorpiones), pseudoscorpions (Pseudoscorpiones), sun or camel spiders (Solifugae), tailless whip scorpions also known as whip spiders (Amblypygi), centipedes (Chilopoda), millipedes (Diplopoda), ticks and mites (superorders Parasitiformes and Acariformes), springtails (Collembola), bristletails (Zygentoma), and isopods (Isopoda).

In evolutionary terms, arthropods are very successful animals that have adapted to every type of habitat and have utilized diverse ecological niches, adjusting their body sizes accordingly over time. While there may have been larger prehistoric ancestors of the current arthropods, as can be found in the fossil record, the extant species nonetheless display an impressive size range. The smallest free-living insects are minute wasps known as fairyflies belonging to the family Mymaridae (UAE examples can be seen in Fig. 17.1). In 2019, a new fairyfly species was collected in Hawaii (Huber and Beardsley 2000) that ranges in body length from 0.19 to 0.3 mm in length (190–300 μm), only slightly larger than the width of a human hair. Among the arachnids, the smallest mite is about a tenth of a millimeter. In comparison, the longest insect is a stick insect, with the longest ever recorded measurement being 64 cm, according to Guinness World Records (2018).

Fig. 17.1

These tiny insects, found in a garden in Al Ain in the Abu Dhabi Emirate, are examples of wasps known as fairyflies (Mymaridae) that elsewhere have been recorded as the smallest free-living insects. Due to their small size, the fairyflies were photographed using a dissecting microscope which reveals a key character that helps to identify the wasps to family level, i.e. the presence of ‘feathery’ wings. Photo credit: Brigitte Howarth

In the UAE, arthropods also display a vast array of sizes, with the smallest mites being a fraction of a millimeter long, fairyflies of barely a millimeter in length, and the largest beetle (a longhorn beetle) measuring more than 8 cm in length (Tan and Howarth in preparation). Camel spiders can be as large as a human hand. Arthropods are found throughout the entire range of habitats in the UAE, including some of the most inhospitable environments such as sabkha (Hogarth et al. 2002). Some species can live in a variety of different habitats that occur across the nation (generalists), whereas other species require specific biotic and abiotic conditions and are, therefore, only found in areas suitable to their needs (specialists). Progress has been made in cataloguing UAE arthropod diversity, which is now relatively well-known due to recent work to create a species inventory, published in six large volumes and edited by A. van Harten (editor and author) between 2008 and 2015. This work has added thousands of species to the list of UAE arthropods (van Harten (editor) 2008, 2009, 2010, 2011, 2014, 2015). However, their ecology remains poorly understood, especially those identified as ‘new to science’.

This chapter tells the story of some of the groups of terrestrial arthropods found in the UAE and aims to galvanize readers’ interest in filling the many knowledge gaps. It is necessary to fully understand the complexity of arthropod interactions among themselves, other organisms and their environment—including the myriad of services attributed to local terrestrial arthropods—to be able to engage in meaningful ecosystem conservation.

3 Diversity

The earliest records of Arabian fauna and flora were published in 1775 and were the results of a Danish expedition, sponsored by King Friedrich V, that visited the region between 1762 and 1767 (Büttiker 1979). Many initial insect records, and other fauna and flora are attributed to Peter Forsskål (1775) (Forsskål is spelled in a variety of ways in the literature), who was one of the exploration team members. As a student of Linnaeus, Forsskål had been well trained for the documentation of organisms on this journey. Most of his contributions were published posthumously by Carsten Niebuhr who was the sole survivor of the expedition (Büttiker 1979). Despite the many Arabian destinations visited during the journey, the expedition did not extend to the modern UAE territory. As a result, most arthropod records for the UAE date from the mid-1900s onwards—although many of the UAE’s faunal and floral records were previously recorded elsewhere in Arabia by Forsskål (e.g., the desert locust Schistocerca gregaria; Forsskål 1775). Regional universities have only recently become more research-intensive and, as such, represent a growing but still minor contributor to biodiversity studies. As a result, much of the historical knowledge of the biodiversity of most groups of organisms, including arthropods, has been generated by specialists visiting from other parts of the world, typically Europe and more recently North America (van Lavieren et al. 2011; Vaughan and Burt 2016). Many significant contributions to arthropod records were published between 1979 and1997 in the “Fauna of Saudi Arabia” series (volumes 1–16) which later became “Fauna of Arabia” in 1998, ceasing publication with volume 25 in 2010. Even within the first few pages of the first volume, discussions of arthropod records from the UAE are included, e.g., the scorpion Vachoniolus globimanus recorded from Abu Dhabi (Vachon 1979).

Prior to 2008, arthropod records from the UAE were scattered throughout the literature, with species counts difficult to aggregate. Many records were contributed by members of the Emirates Natural History Group (ENHG) following its official creation in 1976. From January 1977 to November 1990, early records and observations were published in the ENHG newsletter (The Bulletin). The Bulletin later evolved into the ENHG peer-reviewed journal called Tribulus in 1991. This journal continues to be published to the present day, with non-professional members of the ENHG chapters in Abu Dhabi, Al Ain and Dubai contributing a significant number of articles to the publication, but also with articles by other scholars and researchers. In 2008, two key milestones in the study of arthropods occurred: (1) all insect records known from the UAE were consolidated and published in a chapter focused on Abu Dhabi emirate arthropods, with the species count of insects alone reported as 1528 species (Howarth and Gillett 2008), and (2) the same year, the van Harten national arthropod inventory project’s first volume was published. Field and laboratory work and the first four volumes were sponsored by H.H. Sheikh Tahnoon bin Zayed Al Nahyan. Volume 1 was followed by a further five volumes published in 2009, 2010, 2011, 2014 and 2015, respectively. The consolidation of insect records (Howarth and Gillett 2008) together with the arthropod inventory volumes published by van Harten amount to over 4000 records of arthropods currently known from the UAE (Fig. 17.2). This species count should not be considered exhaustive, as new species continue to be identified and records from past literature continue to be uncovered, but it does represent the most comprehensive assessment of UAE arthropod diversity to date. Nevertheless, Fig. 17.2 speaks to the fact that the arthropod fauna of the UAE has only recently been studied in earnest, suggesting that far more in-depth research is needed to shed light on the ecology of the many species we now know to occur in the UAE.

Fig. 17.2

The above depicts amalgamated records of arthropod species diversity in the UAE from 2008 to 2015. The initial species count consolidated by Howarth and Gillett (2008) (shown as *) included both their own and other published records, and show the baseline of knowledge that existed prior to the start of the insect inventory project (see various van Harten references) which added thousands of records new to the UAE, including records of arthropods new to science

The records added by van Harten’s inventory were significant in their own right, however, what should not be understated is the large number of species that were new to science (i.e., previously undescribed globally) (Fig. 17.3). Although it is possible that some of these species may subsequently also be found in other (most likely regional) countries, especially for those species occurring in continuous habitats that cross country borders, they are nevertheless significant, comprising species currently only known from the UAE. At present, however, it is only their occurrence within the Emirates that has been recorded and nothing is known of their ecology—their population sizes, biological interactions, habitat usage or environmental preferences. This means that it is currently impossible to evaluate these species in terms of their conservation status. Given the rapid development of many habitats across the Emirates, this suggests that long-term monitoring and research on arthropods (and many other fauna) should be considered a priority.

Fig. 17.3

From 2008 to 2015 van Harten edited (and contributed as author) a six-volume biodiversity inventory titled ‘Arthropod Fauna of the UAE’, which added a significant number of new species records to the overall knowledge of arthropod diversity, including many that are new to science. Each blue bar accounts for the total number of new species added per volume to the knowledge of arthropod diversity of the UAE. Of the total number of species added to the list by van Harten in the six volumes (2507 species), 17% of the records were species that were new to science (the orange bars make up the number of species per volume that were new to science)

As suggested above, arthropod diversity (both records new to the UAE and new to science) continues to grow as authors continue to contribute new records. For example, the following represent only a fraction of recent contributions to the UAE arthropod diversity records: Al-Deeb et al. (e.g., 2012) and Negm (2014) added new mite records along with ecological information, Cassola et al. (2012) added a species of tiger beetle only otherwise known from Iran and Pakistan, van Andel (2014) and Feulner and Roobas (2015) contributed to the otherwise poorly known spider fauna, and Saji and Whittington (2008) and Dobosz et al. (2017) added to the knowledge of lacewings.

4 Distribution, Habitats and Importance of UAE’s Arthropod Diversity

Ecosystem services provided by arthropods have been linked to the UN Sustainable Development Goals (Dangles and Casas 2019), establishing their importance to humans in a variety of ways, including welfare, health and provision of resources (Brock et al. 2021). Ecosystem services are provided by arthropods in all the varied habitats of the UAE, despite the challenges they may face in its hyper-arid desert environment. To cope with the extreme climatic conditions, arthropods have devised ingenious strategies and adaptations to maximize their success. Whether these are nocturnal strategies, seasonal emergence timing, emergence following rain, or ephemeral life-history strategies, all approaches can be found within the arthropod fauna of the UAE, though for most species, very little local ecological data exists. Discussed elsewhere are the various terrestrial ecosystems found in the UAE (see Chaps. 2 and 6). Ideally, for the purpose of addressing the ecology of the UAE arthropod fauna, each ecosystem should be examined closely to better understand the many complex food webs and other interactions between arthropods and their environment. However, the deficit of ecological data for many of these taxa prevents such a treatment. To highlight the complexity of arthropod ecology in the UAE, some representative examples are mentioned below, focusing on, where known, their ecological role within ecosystems including their distribution and habitat preference.

4.1 Pollination

Pollination is the initial process that is necessary for reproductive success by sexual means in plants. In simple terms, for pollination to occur, the pollen of one flower must find its way to the stigma of another flower of the same species. Chapter 13 highlights the various pollination methods in flowering plants.

Pollination by arthropods is often a byproduct of their search for food, with an incidental benefit to the host plant. When thinking of pollination, many are tempted to think that this service is primarily carried out by social honeybees. Indeed, honeybees do play a part and do occur in the UAE, but many more arthropods are involved globally, including in the Middle East (e.g., Alqarni et al. 2017). Pollination occurs by several physical means (e.g., wind-pollination), but it also occurs through organisms such as birds, bats, and many arthropods e.g., beetles, flies, wasps, moths, spiders, thrips, and many others.

An example of plant pollination by insects, but not social honeybees, in the UAE is the desert campion (Silene villosa) depicted in Fig. 17.4. This annual plant flowers during the spring and is generally found in stable sand and between dunes (Jongbloed et al. 2003). Campion species found in other parts of the world, e.g., Silene alba, begin to open their flowers at dusk and are fully open during the night and into the next morning (Young 2002). Given the right conditions, desert campion can grow as a carpet of plants, and in the early evening in spring this desert annual releases a heady perfume as the buds begin to open. By the following morning, the flowers begin to degrade, and are often seen wilted by the next afternoon. Night-flowering plants such as the desert campion rely mainly on nocturnal pollinators, although they may incidentally benefit from daytime visitors early the following morning. However, a study of bee and wasp flower visits conducted during the daytime in the UAE did not record any visitors to the desert campion (Gess and Roosenschoon 2016). For this reason, it is speculated that the desert campion is mainly pollinated at night by species of noctuid moths, though the specific relationships are yet to be confirmed for the UAE.

Fig. 17.4

The desert campion, Silene villosa, is generally found with its flowers open during the night and is thought to be pollinated by nocturnal moths. Photo credit: Brigitte Howarth

Apart from the desert campion, it is undoubtedly the case that other flowering plant species occurring in the UAE are associated with specialized pollinators, rather than generalists visiting multiple plant species. For example, nectaries of flowers such as locally occurring lavender (Lavandula subnuda) and a UAE species of sage (Salvia aegyptiaca) are only accessible to insects that possess a sufficiently long proboscis (i.e., a tube-like sucking mouthpart) due to the long flower nectary tubes of these plants.

Butterflies and beeflies both have long mouthparts, but just having a long proboscis may not be the only prerequisite for the success of specialized plant-pollinator interactions, as plants have devised more elaborate mechanisms to maximize their successful pollination. Sage flowers possess two modified, lever-like stamens (i.e., the male flowering parts that develop pollen) that are involved in pollen deposition onto a pollinator. As the pollinator pushes into the flower and against the interior of the flower, the stamens bend downwards depositing pollen onto the back of the insect. A study of several sage species in Turkey identified both specialist and generalist bee pollinators, with ecologically specialised sage species being pollinated by only a single bee species (Celep et al. 2020). The study also showed that ecological specialization was correlated with floral traits such as color, corolla length, size and type of staminal-lever mechanisms as well as flowering time. A selection of some plant-pollinator interactions found in the UAE are depicted in Fig. 17.5.

Fig. 17.5

Pollination of wild flowers by insects. The insects represent just a small number of the many that are found foraging for pollen or nectar from wild flowers in the UAE. (a) Arabian Paper wasp (Polistes wattii) visiting Ochradenus aucheri; (b) melliferous (honey producing) wasp Celonites yemenensis on Morettia parviflora; (c) mating oil beetles (Meloidae) on a species of Tribulus; (d) beefly (Bombyliidae) visiting Salvia aegyptiaca; (e) potter wasp (Eumeninae) visiting a species of Echinops; (f) Painted Lady butterfly (Vanessa cardui) on lavender (Lavandula subnuda); (g) bee wolf Philanthus triangulum and a carpet beetle (Dermestidae) on Ochradenus aucheri. Images of interactions a, d, e, f, and g were captured in wadis of the Hajar Mountains. Image b was taken at the base of Jebel Hafit, and the beetles in c were observed at the Dubai Desert Conservation Reserve (DDCR). Photo credits: Brigitte Howarth (a, b, c, e, f, g) and Gary Brown (d)

It is possible that specialized plant-pollinator interactions occur among the insect fauna observed visiting local sage species, and these may not be bees but flies instead. During spring 2019 this author and Dr. Gary Brown observed beeflies (Bombyliidae) on the sage S. aegyptiaca in wadis of the Hajar mountains (Fig. 17.5d). During the time of observation there were virtually no other insect species visiting the plant, suggesting that beeflies may be an important pollinator for this species, rather than bees. More in-depth study is required to confirm whether this insect-plant interaction is specific, which may include analyses of pollen collected from the body of beeflies, measurement of corolla and proboscis lengths, as well as seasonal studies of visitors to the sage plants to identify potential pollinators. In contrast to observations of insect-plant interactions on sage, flowers that are easily accessible for both pollen and nectar feeders attract many different insect species, e.g., the plant Ochradenus aucheri (Fig. 17.5a and g), and are less likely to have specialized pollinators.

Beetles are also frequent pollinators of wild flowers, especially some of the smaller beetles that occur in the UAE, such as ant-like flower beetles (Anthicidae) which superficially resemble ants. These, and other small beetles, are often seen congregating within or on flower-heads. As part of the arthropod inventory project, an account of the ant-like flower beetle species occurring in the UAE was published in 2008, with a total of 25 species recorded, 3 of which were known, and 4 of which were species new to science (Telnov 2008). Some ant-like flower beetles are cosmopolitan and were recorded at various locations throughout the UAE, while some appear to prefer more specific habitats, such as the newly described species Stricticollis desolatius that was only recorded from Wadi Wurayah thus far. However, more detailed ecological information was not recorded for any of the species, as most were collected using passive trapping methods, as is typical when establishing species diversity inventories.

In a pollination ecology study of an acacia tree species in Saudi Arabia, known as Talh (Acacia gerrardii), researchers used active collection techniques to directly establish which flower-visiting insects were involved in pollination by using sweep-netting and hand-picking (Alqarni et al. 2017). Of all the insects collected, 41% were beetles, and included two species that also occur in the UAE: an ant-like flower beetle (Omonadus floralis) and a carpet beetle (Attagenus posticalis). Alqarni (2017) also concluded that the insects that contributed most to flower visitation were members of the wasp and bee family (Hymenoptera), and specifically honeybees, some solitary bees (Megachilidae), and ants. Almost no such studies have been conducted in the UAE, except for a study of flower visits by aculeate wasps and bees in the Dubai Desert Conservation Reserve (DDCR) (Gess and Roosenschoon 2016). Of the 79 species of bees and wasps recorded in the study (which includes areas outside of the DDCR), 25 species were recorded visiting 21 plant species within the DDCR. It should be noted that 11% of the species observed in the study are known to occur only in the Arabian Peninsula, suggesting that regional endemics play an important role in plant pollination. These are of specific interest, as they are most likely to have more specialized foraging behaviors that are worthy of study. Gess and Roosenschoon (2016) concluded that very few species of wasps and bees encountered were, in fact, specialists, adding that the interactions of specialists recorded were not obligate, with the plants not relying on the wasp and bee specialists but that they were likely the most dependable of the pollinators. Relationships such as those observed by Gees and Roosenschoon are important to begin to understand plant-pollinator interactions and many more studies are needed to understand the ecology of flower-visiting insects, including other pollinators such as hoverflies, butterflies, ants, and the insect orders mentioned earlier (e.g., beetles, social and solitary bees and wasps, and moths, among others).

At times, pollination may not be due to arthropod foraging behavior, but rather due to incidental activity that brings the fauna close to flowers, resulting in accidental pollen transfer. For example, spiders are often seen in and around plants, and in some cases are very well camouflaged, waiting to ambush flower-visiting insects (Fig. 17.6). While the impact on pollination success by spiders and other arthropods that incidentally associate with flowers is likely minimal in comparison to pollen and nectar-feeding insects, it should not be underestimated as an ecosystem service that warrants further study.

Fig. 17.6

A crab spider (Thomisidae) waits in ambush on a lavender plant (Lavandula subnuda). Despite its distinct markings, this crab spider remains unidentified. During the observations of this spider, it moved multiple times over the blossoms. Photo credit: Brigitte Howarth

4.2 Nutrient Cycling and Soil Fertility

Despite the appearance of being uniform, sandy desert soil is complex. Within the UAE, a total of 74 soil series have been identified based on aspects such as soil chemistry, physics, mineralogy, and vulnerability to land degradation (Shahid et al. 2014). Soils are composed of biotic and abiotic components, with a large proportion of the biotic components being organisms that interact with soil. It has been estimated that soil fauna may represent 23% of all described organisms globally, of which arthropods form the largest proportion (85%) (Decaëns et al. 2006).

Arthropods found in leaf litter and upper soil horizons include spiders, springtails, pseudoscorpions, millipedes and centipedes, woodlice, insects, mites, and bristletails, all of which occur in the UAE. In some soils globally, the springtails and mites are among the highest in abundance and diversity of the soil arthropod community (Culliney 2013). As soil arthropods can be quite small, studying their ecology can be challenging. Indeed, springtails and mites are among the smallest arthropods in the UAE, measuring between a fraction of a millimeter to two millimeters in length, although a large mite group known as giant red velvet mites also occurs in the UAE (Fig. 17.7b), and can be over a centimeter long. Giant red velvet mites (Dinothrombidium) are known locally as ‘daughter of the rain’ (بنت المطر) as they are often seen on sand dunes following precipitation. In their discussion of a giant velvet mite’s ecology, Tevis and Newell (1962) note that soil particle size is an important factor that affects the organism’s distribution. The authors also note that the organism only emerges from sand following rain, which is in agreement with UAE folklore and the Arabic name. Feeding behavior was rarely observed, although predation on termites has been recorded (Tevis and Newell 1962).

Fig. 17.7

Two arthropods associated with UAE soils: (a) a globular springtail (Family Bourletiellida) collected from a malaise trap in Wadi Shawkha, Ras Al Khaimah, and (b) a velvet mite at the base of a possible termite mound on a sandy track in the Jebel Hafit National Park in January 2023. Photographers: (a) Brigitte Howarth; (b) Gary Brown

Springtails occur in various habitats around the world, frequently found in damp leaf litter, but semi-aquatic species also exist. Despite the UAE’s arid conditions and lack of continuous or deep leaf litter layers that are typically found in temperate regions of the world, to date 18 springtail species have been recorded for the Emirates, with 3 of these being new to science (Barra and van Harten 2009; Schulz and van Harten 2014) (Fig. 17.7a is an example of a UAE springtail). Springtails are soft-bodied invertebrates with a life cycle that begins with an egg that develops into a nymph and then becomes an adult, molting 6–8 times before reaching the mature adult stage. Their name stems from their means of locomotion. A fork-like structure at the end of their abdomen, called a furcula, is used to ‘spring’ the organism away when facing danger or needing to move. When getting ready to jump, the furcula that is tucked under the organism’s body is pushed downwards, and the organism is propelled upwards, spiraling into the air. Springtails feed on fungus, bacteria, fresh and decaying plant material, but also pollen and lichen, with some being predaceous (Macnamara 1924; Poole 1959; Christiansen 1964; Culliney 2013). Springtails therefore contribute to nutrient cycling and soil health in a variety of ways, including the spread of fungal spores through soil. A dry-land springtail Seira ferrarii that occurs in the UAE, but also elsewhere, is a lithophilous (loving/inhabiting stony places) and thermophilous (warmth loving) species (Tosi and Parisi 1990). It has been found at elevations of 566 meters as well as at sea level on a beach (4 m) in Spain (Cipola et al. 2018), and even from sediments below the Black and Mediterranean seas (Da Gama 1966; Jacquemart and Jacques 1980; Shaw et al. 2011). In the UAE, it was recorded from the mountainous Wadi Wurayah and from Sharjah Desert Park, showing some versatility in habitat usage. Another UAE springtail species (Sphaeridia pumilis) is a cosmopolitan species known to be able to survive in many habitats. In contrast, at least one of the three endemic species recorded from the UAE (Denisiella bretfeldi) appears to be habitat-specific, having only been collected in one location (Wadi Maidaq, Fujairah) (Schultz and van Harten 2014). How UAE species are involved in nutrient cycling and soil fertility requires further study.

Soil fertility refers to a soil’s ability to satisfy plant demands for water, nutrients and a suitable substrate in which roots can develop (Culliney 2013). Arthropods are involved in the provision of these conditions through their ability to break down leaf litter (e.g., as performed by springtails described above) and as ecosystem engineers through their burrowing to allow gas exchange for roots. Ecosystem engineers are organisms that can alter the physical character of a habitat, directly or indirectly, facilitating the success of other species (Jones et al. 1994). Soil turnover is considered essential to the development of a soil profile, an ecosystem service commonly provided by ants and termites in arid and semiarid environments (Whitford 2000). A study of the effects of harvester ant (Messorebeninus) nests on the soil and plants in a dwarf shrub community in Kuwait revealed that soil properties changed substantially in the circular zones around the nests of the ant, with elevated levels of nutrients and organic matter recorded (Brown et al. 2012). In addition, plant productivity and richness were reported to be significantly enhanced in these zones, with the researchers concluding that the ant Messorebeninus is an important ecosystem engineer. There are many species of ants in the UAE, including the same species reported by Brown et al. (2012) which was first recorded from the UAE in 1993 (Tigar and Collingwood 1993). However, similar studies to evaluate the importance of this or other ant or termite species on UAE ecosystems have not yet been carried out.

To a lesser degree, arthropods that spend most time on the wing in the air rather than in the soil, but that deposit eggs into sandy habitats, may also contribute to soil health and the maintenance of such ecosystems either by their burrowing activity or through the provision of food for other soil-dwelling organisms. Such an example is the mydas fly Eremomidas arabicus. It is the largest species of mydas fly found in the Arabian Peninsula, with females having a wing length of 17.5–18.2 mm (Dikow 2010). The species is sexually dimorphic, with the males quite a bit smaller and grey in appearance, in contrast with the larger, orange-colored females. Members of this fly family deposit their eggs into sand, behavior which the author observed at Zakher pools, Al Ain, during October 2010. The female, laden with eggs, was finding it difficult to fly, and eventually buried herself up to her neck in sand, presumably in search for optimal areas to oviposit eggs (see Fig. 17.8). Mydas flies appear to be very seasonal in the UAE and are not observed every year. A mydas fly new to science and only discovered in a Nevadan desert in the United States in 2007 appears to be absent in years of drought and was only recorded in years of moderate or heavy rainfall (Rogers and Van Dam 2007), and it is possible that in the UAE E. arabicus follows a similar pattern. In the United States, another species of mydas fly is the only true fly that has been listed as ‘endangered’ under the U.S. Endangered Species Act due to its restricted habitat range and the threat of habitat loss (Rogers and van Dam 2007). Mydas flies in the UAE are likely also vulnerable to habitat loss and degradation, requiring research to learn more about their ecology.

Fig. 17.8

A female mydas fly (Eremomidas arabicus) was observed burying itself deep into the sand by moving backwards and downwards until only the tips of its wings and its head remained outside of the sand. It is suspected that the fly was first probing for suitable ovipositing substrate, followed by egg-laying, as it remained buried for several minutes before lifting out of the sand, probing and searching again a little further away before repeating the burying behavior. This individual repeated this behavior three times before flying away. Photo credit: Brigitte Howarth

4.3 Population Regulation

In the context of food webs, the presence of many trophic levels (i.e., feeding strategies) in a given ecosystem could indicate complex habitat structures, synonymous with a diverse and functioning ecosystem. Arthropods are involved at many trophic levels, providing valuable services and energy sources for other invertebrates and vertebrates alike. While there have been some studies of species assemblages in the UAE (e.g., Hogarth et al. 2002), more studies of trophic levels found within species assemblages of different local habitats are needed. Yet, many observations have been noted on predator-prey interactions that can be considered as ecosystem services through population regulation. Such an observation was made by Gillett (2009), who identified possible prey species of some ground beetles (Carabidae) found in the UAE. Predatory arthropods of the UAE include spiders, scorpions, camel spiders, beetles, dragonflies, flies, wasps, lacewings, mites, pseudoscorpions, centipedes, and many others, although most have yet to be studied in depth. Camel spiders (Fig. 17.9) include some of the largest arthropods found in the UAE, yet they are also among the most elusive. Camel spider ecology is generally poorly known (Punzo 1998). In a study comparing the functional morphology and bite performance of two camel spider genera from Egypt and Morocco, researchers were able to show significant differences, suggesting possible specialization on prey species (van der Meijden et al. 2012). Camel spiders macerate arthropod prey with powerful jaws without immobilizing their prey with venom as is the case with other arachnids (van der Meijden et al. 2012). The authors investigated anatomical differences as well as bite performance. Both genera investigated are represented in the UAE and have been observed in specific habitats, with Galeodes frequently encountered in sandy areas, and Rhagodes recorded from rocky areas such as mountains or gravel plains. Further study would not only contribute important information on the ecological role of camel spiders, but shed much needed light on their biology.

Fig. 17.9

Camel spiders are generally poorly known which could be due to their great agility, and mainly nocturnal nature. The individual photographed belongs to the genus Galeodes and was found in the sandy habitat of Wadi Nabbagh, Al Ain. Photo credit: Brigitte Howarth

Another arthropod group that is usually overlooked when considering ecosystem services is aculeate wasps. Wasps in this group possess a stinger. The stinger is a modified egg-laying structure or ovipositor. In addition to the pollination services of wasps that were discussed above, wasps also hunt other arthropods, either as predators or as parasites that lay their eggs on or within other organisms (Goulet and Huber 1993; Grissell 2010). This interaction provides a regulatory service, limiting populations of the arthropod prey or host species (Fig. 17.10 depicts the social paper wasp Polistes wattii consuming a mydas fly at Zakher Pools, Al Ain).

Fig. 17.10

Regulatory ecosystem services are frequently provided by members of the aculeate Hymenoptera, such as the paper wasp Polistes wattii. During 2010 when observations of mydas fly egg-laying were made, a paper wasp was recorded devouring a female mydas fly. Photo credit: Brigitte Howarth

Wasps and bees are either social or solitary, with far more known about social bees and wasps in comparison to solitary members of this group. Brock et al. (2021) provide a detailed review of ecosystem services provided by aculeate wasps, stating that solitary wasps are, by far, the most diverse group of wasps, making up approximately 97% of all wasps. Gess and Roosenschoon (2016) list 53 species of aculeate wasps in their study of the Dubai Desert Conservation Reserve (DDCR) and other localities, with 39 of these visiting flowers and likely providing important pollination services. Many of the observed species are likely contributing to regulatory ecosystem services by preying on or parasitizing other insects. Other wasps involved in such ecosystem services are parasitic wasps belonging to families such as the Ichneumonidae, Braconidae and the superfamily Chalcidoidea, all of which are represented in the UAE.

Some of the most agile predators in the UAE are among the Odonata (dragonflies and damselflies) (see Fig. 17.11 for differences between dragonflies and damselflies); both the aquatic larvae and the aerial adults are predacious. The Odonata is likely the insect order that has been most intensively studied in the UAE, with key contributions including Giles (1998), Feulner (1999), Feulner et al. (2007), Reimer et al. (2009), Campbell and Reimer (2011), Reimer (2011), Feulner and Judas (2013), Campbell (2017), Lambret et al. (2017) and others. These authors have added much information with regards to distribution and ecology that highlights the importance of freshwater habitats in the UAE, which are utilized by larvae of this group until they are developed to the stage where they can emerge as adults. For example, Lambret et al. (2017) contributed detailed descriptions of habitat use and mating behavior, though observations of feeding behavior remain sparse. Of note is the assessment of conservation status of Odonata occurring in the Arabian Peninsula (Schneider and Samraoui 2015). One species of the assessed taxa was listed as ‘Critically Endangered (CR)’, nine as ‘Endangered’ (EN), five as ‘Vulnerable’ (VU) and four species as ‘Near Threatened’ taxa (NT). Of these 19 species, 6 are considered endemics that only occur in Arabia. A further 32 species are listed as ‘Least Concern’ (LC), with 8 species not categorized or listed as being data deficient (DD). Of 59 species examined, 23 occur in the UAE. Schneider and Samraoui (2015) list the main threats to Odonata as including rapid development and modifications to natural systems such as the creation of dams, water abstraction, the destruction of riparian habitats, pollution, agriculture and aquaculture. The listed threats that are impacting the Odonata are also serious threats for the many other arthropod species that are dependent on aquatic ecosystems in the UAE (many insects, for example, have aquatic larval phases and cannot complete their life cycle without access to freshwater). As Odonata contribute to regulatory ecosystem services, the threats listed could potentially impact key foodweb interactions, modifying species dynamics in freshwater ecosystems of the UAE.

Fig. 17.11

The insects depicted both belong to the order Odonata which includes both (a) damselfies and (b) dragonflies. Damselflies are usually slenderer in comparison to dragonflies and hold their wings over the abdomen when at rest, as is seen in the first image (a) depicting a male Evan’s Bluetail damselfly (Ischnura evansi), whereas dragonflies spread their wings out while perched or at rest. The second image (b) depicts an immature male Gulley Darter dragonfly (Trithemis arteriosa), which will turn red on maturity. Photo credits: Brigitte Howarth

Arthropods in the UAE are beneficial to other organisms that either feed on their dead bodies as detritivores, or that actively hunt them as food, such as reptiles, small mammals and birds. A longhorn beetle species that occurs in the UAE is the largest beetle species found regionally. The beetle, Anthracocentrus arabicus, was largely unnoticed for many years, with only carcasses of dead beetles found at the base of Ghaf trees (Prosopis cineraria). In recent years, this author and Dr. M. Gillett, and later the author and Dr. J. Tan, conducted studies to learn more about this species (e.g., Tan and Howarth in prep.). Observations of note, captured in Fig. 17.12, included the impalement of a longhorn individual on a spike, with most of the body missing. Tan and Howarth observed a shrike species in the vicinity and conclude that the longhorn beetle likely forms part of this bird’s diet. Another observation was the presence of A. arabicus remains in eagle owl pellets, suggesting that they may represent an important prey species for eagle owls. Both observations add valuable ecological data for an otherwise poorly known species.

Fig. 17.12

A rare sighting of a female longhorn beetle (Anthracocentrus arabicus) ovipositing into sand (a); (b) the head and thorax remains of a longhorn beetle impaled on a desert shrub suggests that this species forms part of the diet of a shrike species; (c) evidence of longhorn beetle remains in eagle owl pellets provide evidence that A. arabicus forms part of the diet of eagle owls. Photo credits: Brigitte Howarth

5 Threats to UAE’s Arthropod Diversity

In 2020, a landmark assessment of global insect population trends revealed what many had suspected for a long time: insect populations are in drastic decline (Wagner et al. 2021), with an annual abundance decline of 1–2% reported. The study also summarizes the most likely stressors involved, including climate change, pollution and insecticides, alien or introduced species, agricultural intensification, deforestation of the tropics and urbanization, with the last three stressors leading to habitat loss, degradation and fragmentation. Many of the same stressors occur in the UAE (Gardner and Howarth 2009), with the loss of terrestrial habitat being the main concern, such as through widespread quarrying activities that have resulted in the loss of pristine mountain and wadi habitats in the Hajar range (see also Chap. 6). While Wagner et al. (2020) were able to base their assessment on a myriad of studies from many countries, there currently is no monitoring study (past or ongoing) with sufficient baseline information to assess the stressors behind potential arthropod loss in the UAE. This author has been involved in a 5-year malaise trap arthropod study in a mountain wadi (Fig. 17.13), along with a 1-year malaise trap study of Ghaf trees (Prosopis cineraria) in the sandy habitats of the Dubai Desert Conservation Reserve (DDCR), with information that will likely provide valuable insights about composition and trends in arthropod communities in the Emirates.

Fig. 17.13

Studying species abundance is often conducted using passive trapping methods, such as the tent-like malaise trap shown here. Flying insects usually fly into the middle of the trap, not seeing the transparent fabric, and then will attempt to fly to the highest point towards the sun to escape. The front part of the malaise trap is higher than the back with an opening in it, allowing insects to pass through into the receptacle that contains 70% ethanol. Many non-flying arthropods have been sampled this way, including spiders, camel spiders, scorpions, mites and springtails. Photo credit: Brigitte Howarth

Some species will suffer more than others in the UAE due to their specific habitat requirements. For example, several of the UAE’s tiger beetles, such as Callytron monalisa, first recorded from the UAE in 2007 (Cassola et al. 2012), live and reproduce on intertidal mudflats and adjacent sandy shores that occur along the Arabian Gulf coast of the UAE (Feulner and Roobas 2014), a habitat under threat from coastal development (Burt 2014). Another beetle species threatened by the consequences of habitat loss is the longhorn beetle, Anthracocentrus arabicus, discussed above. This is a large longhorn beetle species that is associated with Ghaf trees. Ghaf populations are found in dune habitats mainly in the north-east of the UAE, with increasing amounts of their habitat fragmented by roads and urbanization. This encloses local individuals or populations within a ‘Juzur’ or habitat island, restricting the capacity for dispersal of many species associated with Ghaf ecosystems. This, in turn, can lead to genetic isolation, which could lead to the loss of species such as A. arabicus, impacting not only the beetle but its ecosystem function within the habitat, where it forms an integral part of food webs. While some biological information is available for the above two beetle species, such information remains unknown for many arthropods in the UAE, making it more difficult to assess the impact of stressors on their populations and therefore the ecosystems they inhabit.

In the case of total loss or severe degradation of habitats, such as that caused by quarrying, the impacts are extremely concerning, especially for species associated primarily with mountain and wadi systems, which includes most of the UAE’s dragonflies and damselfies. The Desert Basker dragonfly (Urothemis thomasi) was only recently added to the UAE faunal list (Feulner and Judas 2013). It was recorded from Wadi Wurayah on the East Coast of the UAE in the Hajar Mountains. Some Odonata are among the few arthropods occurring in the UAE for which an IUCN status exists. For example, the Desert Basker has been assessed as decreasing globally and is classified as ‘endangered’ (Boudot 2018). While Wadi Wurayah is a protected area and has more permanent water than other UAE wadis, it is very likely that the Desert Basker will be found in other mountain wadis along the UAE’s Hajar Mountains. Further habitat loss through quarrying could, therefore, impact its status even further, along with many species that have not yet been assessed.

As well as habitat destruction, many of the tourism and leisure activities that occur throughout the UAE are of concern. With regard to sand dunes, the many organisms that live within the top layer of the sand are specifically under threat. The mydas fly Eremomidas arabicus depicted in Fig. 17.8 lays its eggs in the upper sand, between 4 and 8 cm into the substrate. ‘Dune bashing’ and off-road driving activities churn up and compact sand, very likely causing damage or death to organisms that live in it, including arthropods. While hiking itself is usually not destructive, wading through freshwater pools with sunscreen could potentially leave an oily residue on the surface of pools, with many individuals crushed and their habitat, eggs and larvae disturbed through the activity.

Land-use changes include habitat remodeling, such as the creation of artificial lakes. In several of the emirates, artificial bodies of water have been created, whether to store runoff or grey water, or for amenity. This can cause displacement of species that had utilized that habitat, although they may serve as a water body for other species requiring water for the aquatic larval portion of their life cycle. Malaise trap studies of sandy habitats in Dubai Emirate have shown that most of the arthropod biomass near artificial lakes differs in species diversity and evenness usually found in sandy habitats, with an overall decrease in arthropod diversity but an increase in biomass of species that rely on water for parts of their life cycles such as midges and mosquitos (personal observation).

An additional concern is the lack of IUCN Red List extinction threat assessments for arthropods globally. This is likely due to the sheer numbers of arthropods and the difficulty associated with studying their populations. Nevertheless, this makes the evaluation of their status difficult, and impacts most arthropod groups, with few exceptions. Because many UAE ecosystems have not been studied in detail and their species assemblages are largely unknown, it is therefore also difficult to evaluate the impact on shifts and losses of ecosystem functioning caused by stressors and the consequences for fauna and flora that rely on arthropods either for ecosystem services or as a food source.

6 Conservation and Future Research

Sandy deserts are often described with words such as ‘barren’ or ‘hostile’. This creates an association of a landscape that is devoid of life and not worth considering in conservation efforts. In the first instance, a paradigm shift needs to occur to move away from this association to recognize that the word ‘desert’ describes a biome that lacks regular precipitation and is therefore associated with periods of drought. While this does mean that fewer organisms live in such habitats in comparison to tropical rainforests, it does not mean that deserts are barren. On the contrary, organisms found in such a habitat are specifically adapted to cope with the abiotic stresses they face. Conservation efforts for arthropods involve ecosystem approaches rather than a focus on a particular species, because arthropods are part of complex food webs involving many taxa and their environments. As is evident from this account, there is a poor understanding of food webs of organisms in the UAE and the role that arthropods play in them, which means that conservation efforts here would have to rely on the findings of studies carried out in foreign desert environments. Yet, vegetation composition, geology, topography and weather conditions are specific to the UAE, as is elaborated on in Chaps. 2, 3 and 5. Except for very few of the arthropod groups mentioned in this chapter, the life histories, habitat requirements, interactions and conservation status of most UAE arthropod species remains largely unknown. As elaborated earlier, thanks to the six volumes edited and contributed to by van Harten et al., as well as other professional and amateur contributors, a reasonable arthropod inventory now exists. Although this, too, remains incomplete, with some habitats continuing to be under-studied (e.g. gravel plains). Equally, there currently is no definitive local arthropod specimen reference collection in the UAE that can easily be consulted, which is an additional obstacle (although this will be addressed with the establishment of the Natural History Museum Abu Dhabi, currently under construction).

Just as habitat fragmentation and destruction leads to species loss globally, the same is likely the case here in the UAE. Many mountain, wadi, coastal and inland sand dune habitats have been lost through development and urbanization, though there are still vast sand seas south and west of Abu Dhabi, which can be considered ancient in nature. Though new dunes form frequently from shifting sands, much of the inland sand seas consist of Quaternary sand with older underlying geology (Glennie 2005). Ancient, reasonably undisturbed, habitats are becoming rarer globally as most land surfaces have been transformed in one way or another by human activity. The ancient mountain and sand habitats of the UAE contain a vast array of arthropod communities that have evolved over time to survive under hyper-arid conditions. These intact communities require in-depth study to understand how they continue to exist under such conditions.

The limestone and ophiolite mountains and wadis of the UAE are home to large numbers of plants with many arthropod-plant interactions both above and below ground, but these interactions remain to be studied, and the heavy overgrazing likely represents a substantial threat to the vegetation that supports the arthropod communities and wider food webs in these areas (see Chap. 5). An urgency, therefore, exists in the UAE to study arthropods whilst remnants of these habitats still exist. The large number of species recently recorded as new to science from the UAE is exciting, as these can be considered endemic to the UAE or eastern Arabia. All require in-depth study. Arthropods are often difficult to locate due to their varied life history strategies such as being seasonal, nocturnal or burying in strata such as mudflats or sand. Many species have evolved complex life histories to ensure their survival. Some species occurring in the UAE may be indicator species of undisturbed local environments or be keystone species, but more information is needed on their life histories, and interactions within food webs, before such designations can be made. Within each of the larger habitats there are smaller microhabitats such as ephemeral pools of water, blossoming regional trees, or tributary wadi habitats. To fully comprehend how arthropods are contributing to the survival of healthy ecosystems, microhabitats and their associated arthropod communities must be described, and species interactions recorded and studied. Studies of arthropod communities require long-term monitoring to tease out whether changes to species assemblages are due to long-term trends (e.g., climate change or habitat loss) or to the variable year-to-year dynamics of processes like rainfall and drought. Such data is complex and only possible to understand through long-term monitoring. This does mean that there are many opportunities for further study of the arthropods of the UAE. Once more ecological knowledge exists, it will contribute to effective ecosystem conservation planning, and possibly to habitat restoration.

7 Conclusion

The current account of arthropod ecology in the UAE is intended to provide a brief overview of some of the interactions that are known, along with the many unanswered questions that remain in the hope that others will endeavor to attempt to add to the existing body of knowledge.

8 Recommended Readings

While not meant to be exhaustive, additional resources for the UAE arthropod fauna can be found in a variety of publications, such as Feulner et al. (2021) for butterflies, van Harten’s Arthropod Fauna of the UAE volumes (2008–2015), and papers in the nearly 30 volumes of the journal of the Emirates Natural History Group, Tribulus (available online at http://enhg.org/) e.g., Feulner and Roobas (2015) for spiders. In other publications as discussed in the text above, Saji and Whittington (2008) have contributed to the knowledge of antlions, and Howarth and Gillett (2008) summarized a general overview of arthropods that occur in the Abu Dhabi Emirate, applicable to the UAE as a whole.