Atlas of ticks (Acari: Argasidae, Ixodidae) in Germany: 1st data update

The first data update of the atlas of ticks in Germany published in 2021 is presented here. This atlas provides maps based on georeferenced tick locations of 21 species endemic in Germany as well as three tick species that are regularly imported to Germany. The data update includes the following numbers of newly georeferenced tick locations: 17 Argas reflexus, 79 Carios vespertilionis, 2 Dermacentor marginatus, 43 Dermacentor reticulatus, 4 Haemaphysalis concinna, 3 Haemaphysalis punctata, 3 Hyalomma rufipes, 3 Ixodes apronophorus, 9 Ixodes arboricola, 1 Ixodes ariadnae, 30 Ixodes canisuga, 3 Ixodes frontalis, 80 Ixodes hexagonus, 3 Ixodes lividus, 497 Ixodes ricinus/inopinatus, 1 Ixodes rugicollis, 17 Ixodes trianguliceps, 14 Ixodes vespertilionis, and 45 Rhipicephalus sanguineus sensu lato. Old and new tick findings were mapped, such as the northernmost occurrence of D. marginatus in Germany observed in 2021, but also the historical records from the first descriptions of I. apronophorus and I. arboricola, which were georeferenced here for the first time. The digital dataset of tick locations available for Germany is supplemented by 854 new tick locations. These records increase the number of tick species mapped in the federal states Bavaria, Brandenburg and Mecklenburg Western Pomerania by five each, those in Berlin and Schleswig-Holstein by four each, those in Hamburg by three, those in Baden-Wuerttemberg, Bremen, Lower Saxony, Northrhine-Westphalia, Rhineland Palatinate and Thuringia by two each, and those in Hesse, Saxony and Saxony-Anhalt by one each. Thus, the first data update of the tick atlas in Germany and the underlying digital dataset significantly improve our knowledge of the distribution of these tick species and helps to investigate the effects of climate change and habitat changes on them. Supplementary Information The online version contains supplementary material available at 10.1007/s10493-023-00784-5.

Knowledge gaps in Rubel et al. (2021) were due to the fact that some relevant papers on ticks have not been written in English and, moreover, old articles and former journals are often not available in digital form. Much of the references used here can therefore not be found through common database queries, but only through expert knowledge. In addition, the lockdown in 2020/2021 caused by the COVID-19 pandemic made it more difficult to obtain literature from libraries that restricted their services or were completely closed (Nicola et al. 2020). Therefore, for example, the locations of the short-legged bat tick C. vespertilionis (Rupp et al. 2004) could only be assigned to the federal state of Bavaria. Due to the work of Sándor et al. (2021) geographical coordinates are now available. Some colleagues reacted to the atlas of ticks in Germany by pointing out the occurrence of ticks that were not taken into account by Rubel et al. (2021) by making their own studies accessible (Henkel et al. 1983). Last but not least, the historical work of Paul Schulze was included in the tick atlas. For example, the finding of I. apronophorus from the first description by Schulze (1924) and several findings of I. arboricola from the first description by Schulze and Schlottke (1929) have been georeferenced. Data from the publications mentioned, numerous other previously unavailable data sources and new tick findings of the authors might justify this data update, with which further gaps in the mapped tick occurrence in Germany have been closed. For this purpose, the new georeferenced locations and the updated distribution maps are presented here.

Data and methods
The data used here are georeferenced tick locations in Germany described by Rubel et al. (2014Rubel et al. ( , 2021 supplemented by 854 new records. The geographical coordinates of the new tick locations are provided in the supplement together with an indication of their accuracy and the sources. The coordinates are given in decimal degrees with a measure of accuracy identical to those previously introduced by Rubel et al. (2014Rubel et al. ( , 2018Rubel et al. ( , 2021. The tick locations are mapped using R, a language and environment for statistical computing (R Development Core Team 2019). Artificial data clusters caused by single studies were reduced using a random selection and a thinning algorithm (Aiello-Lammens et al. 2019). For example, the newly georeferenced tick locations of the study by Centurier et al. (1979) and Hoffmann (1981) significantly increased the number of R. sanguineus sensu 1 3 lato reports. However, only 42 out of 76 known locations were mapped to avoid overlapping location points.
Tick species, for which only a few locations are known, are grouped according to their host preferences as proposed by Hornok et al. (2020). For example, the bat ticks C. vespertilionis, I. ariadnae, I. simplex, and I. vespertilionis are shown in the same map.

Results
The outcomes of this study are updated geographical maps that depict the occurrence of all tick species that have so far been reported in Germany. It should be noted that the widespread I. inopinatus (Hauck et al. 2019) has been combined with I. ricinus and they are called I. ricinus/inopinatus hereinafter as in Rubel et al. (2021). The improvements resulting from the data update are summarized in Table 1. Accordingly, the first data update increases the number of tick species mapped in the federal states Bavaria, Brandenburg and Mecklenburg Western Pomerania by five each, those in Berlin and Schleswig-Holstein by four each, those in Hamburg by three, those in Baden-Wuerttemberg, Bremen, Lower Saxony, Northrhine-Westphalia, Rhineland Palatinate and Thuringia by two each, and those in Hesse, Saxony and Saxony-Anhalt by one each. All tick species are presented below with a brief summary of the numbers of updated locations compiled for this study. If the ticks were collected from hosts, these are also mentioned. For information on the global distribution, biology, hosts, as well as the medical and veterinary importance of the tick species identified in this paper the reader is referred to Petney et al. (2012Petney et al. ( , 2015 and Rubel et al. (2014Rubel et al. ( , 2021.

Dermacentor marginatus (Sulzer)
Two new locations of the ornate sheep tick D. marginatus were added to the distribution map. An adult male picked up by a woman south of Düsseldorf represents the new 1 3 northern distribution limit of D. marginatus in Germany at a latitude of 51.02 • N (determined by Olaf Kahl, 2021). Recent records from a citizen science study indicate that D. marginatus may occur even a bit further north . The second new tick location was reported by Weigand et al. (2023). A total of 95 out of 120 known locations is mapped in Fig. 3.

Dermacentor reticulatus (Fabricius)
The following 43 locations were added to the distribution map of the ornate dog tick D. reticulatus: 1 (Negrobov and Borodin 1964), 1 (Maasjost 2006), 19 (Liebisch and Liebisch 2007), 4 (Schreiber et al. 2014), 9 (Rehbein et al. 2016, 1 (Ott et al. 2020), 1 (leg.  Ixodes ricinus  (Maasjost 2006), the updated distribution map shows D. reticulatus findings in all federal states except Hamburg and Schleswig-Holstein. However, new records from a citizen science study were recently published for these federal states, which prove the Germany-wide occurrence of D. reticulatus ). Since D. reticulatus has been found in Hamburg and Schleswig-Holstein but no 1 3 georeferences are available, its occurrence is marked as a circle in Table 1. A total of 228 out of 404 known locations is depicted in Fig. 4. 1 3

Haemaphysalis (Aboimisalis) punctata Canestrini and Fanzago
The following three locations were added to the distribution map of the red sheep tick Ha. punctata: 1 (Koch 1877), 2 (Hesse and Völker 1983). The tick findings of Hesse and Völker (1983) were reported from Siegaue near Bonn. The meadow landscape of Siegaue is known as a resting place for migrating coastal birds, which might be why Ha. punctata was probably introduced by them. The ticks were collected from a stone marten (Martes foina) and flagged from the vegetation. The infestation of a human was also documented. The ticks found by Koch (1877) were collected near a lake at Dutzendeich, Nuremberg. The tick species described under the synonym Rhipicephalus expositicius is clearly Ha. punctata (Schulze 1925). A total of six known locations is mapped in Fig. 5. 1 3

Hyalomma (Euhyalomma) marginatum Koch
No locations were added to the map of Hy. marginatum. A total of 14 known locations is depicted in Fig. 6. 1 3

Hyalomma (Euhyalomma) rufipes Koch
The following three locations were added to the map of the hairy or coarse bont-legged Hyalomma tick, Hy. rufipes: 3 . A total of 11 known locations is depicted in Fig. 6. 1 3

Ixodes (Ixodes) acuminatus Neumann
No locations were added to the distribution of I. acuminatus. A total of three known locations is depicted in Fig. 7.

Ixodes (Ixodes) apronophorus Schulze
The following three locations were added to the distribution map of I. apronophorus: 1 (Schulze 1924), 1 (Negrobov and Borodin 1964), 1 (Aeschlimann et al. 1970). The location of I. apronophorus from the first description by Schulze (1924) could be assigned to the Kremmener Luch nature reserve in Brandenburg. A total of five locations is depicted in Fig. 7.

Ixodes (Pholeoixodes) arboricola Schulze and Schlottke
The following nine locations were added to the distribution map of I. arboricola: 4 (Schulze and Schlottke 1929), 1 (Schulze 1937), 1 (Schilling et al. 1981), 3 (Walter 1992). Among other places, Schulze (1932) reported I. arboricola from the Harz. The Harz is the highest mountain range in northern Germany (elevation: 1141 m). It lies at the intersection of Lower Saxony, Saxony-Anhalt and Thuringia. Since there are no georeferenced locations of I. arboricola for Saxony-Anhalt and Thuringia, its occurrence is marked as a circle in Table 1. A total of 29 known locations is depicted in Fig. 8.

Ixodes ariadnae Hornok et al.
The following location was added to the distribution map of I. ariadnae: 1 Weigand et al. (2023). At this new location near Friedewald, Hesse, one nymph of I. ariadnae was found in each of the winters of 2021 and 2022. A total of two known locations is depicted in Fig. 2.

Ixodes (Trichotoixodes) frontalis (Panzer)
The following three locations were added to the distribution map of I. frontalis: 1 (Stadler and Schenkel 1940), 1 (Walter et al. 1979), 1 . A total of 65 out of 92 known locations is depicted in Fig. 8.

Ixodes (Pholeoixodes) hexagonus Leach
The following  low-resolution map of Germany presented here, although the georeferenced coordinates are provided in the supplement. A total of 217 out of 397 known locations is depicted in Fig. 10.  have not differentiated between I. ricinus and I. inopinatus and reliable differentiation of both species is very difficult, the two species are combined herein and referred to as the I. ricinus/inopinatus species complex. Moreover, a recent study based on genomic data indicates that German I. inopinatus samples may represent I. ricinus (Rollins et al. 2023). Consequently, it seems that the morphological and mitochondrial genome-based methods used so far are not sufficient to distinguish between I. inopinatus and I. ricinus. A separate map for I. inopinatus was therefore not compiled. 1 3

Ixodes (Pholeoixodes) lividus Koch
The following three locations were added to the distribution map of the nest-dwelling bird parasite I. lividus: 2 (Schulze and Schlottke 1929), 1 (Stadler and Schenkel 1940). Müller (1977) described the occurrence of I. lividus in the former district of Magdeburg (former GDR). In the breeding periods 1972-1976 more than 1,800 sand martins Riparia riparia and some of their burrows were examined in various unspecified sand pits. The proportion of sand martins infested with I. lividus varied greatly from year to year between 0.7 and

Ixodes (Pholeoixodes) rugicollis Schulze and Schlottke
The historical Berlin location by Schulze and Schlottke (1929) was added to the distribution map of I. rugicollis. Since there is no exact location for this finding, the point in the map is to be interpreted symbolically for the occurrence of I. rugicollis in Berlin. Consequently, I. rugicollis was not mapped in the high-resolution city map of Berlin . A total of six known locations is depicted in Fig. 8.

Ixodes (Pomerantzevella) simplex Neumann
No location was added to the occurrence of I. simplex in Germany. The only up to now known location is depicted in Fig. 2.

Ixodes (Ceratixodes) uriae White
No location was added to the occurrence of the seabird tick I. uriae in Germany. One known location is depicted in Fig. 1. 1 3

Rhipicephalus sanguineus (Latreille)
The following 45 locations were added to the occurrence of the brown dog tick R. sanguineus sensu lato: 35 (Centurier et al. 1979), 10 (Hoffmann 1981. A further study concerning 60 dogs infested with R. sanguineus s.l. documented the occurrence of the brown dog tick in eight federal states in West Germany (Gothe 1999). No exact location information was given in this study. However, the study documents the occurrence of R. sanguineus s.l. in another federal state without georeferenced locations, namely Rhineland Palatinate (Table 1). A total of 42 out of 76 known locations is mapped in Fig. 6.

Discussion
The greatest progress compared to the first version of the atlas of ticks in Germany (Rubel et al. 2021) was made in mapping the bat ticks C. vespertilionis and I. vespertilionis. The previous atlas of ticks in Germany showed 32 locations of the short-legged bat tick C. vespertilionis, but these were almost all in the northwest of Germany. With another 79 locations of C. vespertilionis it could be shown that this tick is widespread almost all over Germany (Fig. 2). The five locations of the long-legged bat tick I. vespertilionis described by Walter and Kock (1985) could be supplemented by another 14 locations. Both the bats and the caves they inhabit are now under strict protection and scientific surveillance. However, there is little ongoing work on bat ticks in Germany, and ticks found in caves are only a side result of those investigations (Weigand et al. 2023). Nevertheless it can be assumed that I. vespertilionis is by no means rare, as the findings in numerous karst caves in the neighbouring countries Austria (Rubel and Brugger 2022) and Belgium (Obsomer et al. 2013) indicate.
With the georeferencing of 47 locations from Centurier et al. (1979), the map of R. sanguineus s.l. could also be significantly improved. Findings of R. sanguineus s.l. were reported from the metropolitan areas of Frankfurt/M., Hanover, Munich, Berlin and also from some other areas (Fig. 6). It is striking that all these findings of R. sanguineus s.l. are located in the former Federal Republic of Germany and in the former Berlin (West). The majority of these records date from before 1990, when people from the former East Germany were usually not allowed to visit Mediterranean or any subtropical countries. In contrast, the two Hyalomma species are brought to Germany via migratory birds in each spring and have been found all over the country. But because all these cases most probably reflect single (temporary) cases of importation, we do not talk about distribution. From an ongoing citizen science project (Fachet et al. 2020) 10 findings of R. sanguineus s.l. in Germany have been presented (not mapped), so even more current data are known. Because R. sanguineus s.l. in Germany usually occurs inside houses of people and quickly becomes irritating to the inhabitants, their presence might be in most cases only short-lived due to the control measures that have been introduced.
The data update also expands the knowledge of the distribution of those tick species, for which only a few new locations have been georeferenced. For example, with a new finding in Pulheim south of Düsseldorf (leg. Olaf Kahl, 2021) the northern distribution limit of D. marginatus in Germany shifts to the geographical latitude of 51.02 • N. With the georeferencing of a location from the map of Maasjost (2006) the occurrence of D. reticulatus in Bremen has been documented. With updated reports of the red sheep tick Ha. punctata (Koch 1877;Hesse and Völker 1983) it is documented that this originally Mediterranean tick species occurs at the resting places of migratory birds on their way to Northern Europe. As a result, Ha. punctata is widespread on the North Sea coast of England (Tijsse-Klasen et al. 2013), the Netherlands (Hofmeester et al. 2016), and Germany (Fig. 5). The 17 newly georeferenced locations of the rarely investigated vole tick I. trianguliceps indicate its occurrence throughout Germany. Finally, the distribution map of the best-studied tick, I. ricinus, was updated to 915 plotted locations now (Fig. 11). It seems quite certain that areas without any data points of I. ricinus in few parts of Germany probably mirror missing investigation rather than unsuitable areas for this tick species, e.g. parts of Schleswig-Holstein in northern Germany. Mountainous areas above an altitude of 1200 m might also be an exception.
Looking at the tick data presented here from the perspective of climate change, it seems that there have been only minor effects on the German tick fauna, as yet. However, D. reticulatus has been found much more frequently and in much larger numbers in parts of northern Germany in the past 2-3 decades than before. It is unclear to what extent this effect is due to climate change or habitat modification. Kahl and Dautel (2013) suggested that D. reticulatus might profit from increasing temperatures at its northern edge of distribution because development from oviposition to the F1 adult stage must take place within only one growing season in this species. The tick D. marginatus, which was clearly restricted to the mild climate of the Rhine-Main area, also seems to have expanded its range somewhat to the north.

Conclusions
The first data update of the atlas of ticks in Germany is presented here. Greatest progress compared to the first version was made in mapping the occurrence of the ticks C. vespertilionis, R. sanguineus s.l., I. arboricola, I. hexagonus, I. trianguliceps, and I. vespertilionis. The data update also expands knowledge of the distribution of rare tick species. In individual federal states, the number of documented tick species has increased by up to five. Thus, the first data update of the tick atlas in Germany and the underlying digital dataset in the supplement significantly improves our knowledge of the distribution of tick species and may be useful for future investigations to determine the effects of climate change and habitat changes on them.