1 Introduction

Social wasps (Vespidae: Polistinae) exhibit fascinating predation habits that play a crucial role in their ecosystem. These wasps are omnivorous, preying on a wide range of organisms, such as insects and spiders, and drinking nectar from flowers (Sühs et al. 2009; Somavilla et al. 2016; Prezoto et al. 2019). Wasps are generally highly efficient hunters, using their powerful stingers to paralyze or kill their prey. Once a wasp captures its prey, it brings it back to the nest to feed the developing larvae, contributing to brood survival. This predation behavior not only ensures the wasps’ sustenance but also helps control pest populations in their habitat, for example, when performing predation of lepidopteran larvae species recognized as agricultural pests (Prezoto et al. 1994; Bichara Filho et al. 2010; Jeon et al. 2019). The foraging behavior of wasps highlights their ecological significance as both predators and, when they visit flowers, as pollinators (Vieira and Shepherd 1999; Sühs et al. 2009; Prezoto et al. 2019; Elisei et al. 2021).

Polybia ignobilis (Haliday 1836), a species commonly found in South America, ranging from Panama to South Brazil and Argentina (Carpenter and Marques 2001), is a social wasp well-known for its aggressive hunting and stinging behavior (Richards 1978). These wasps construct nests that are protected by envelopes and are typically situated in cavities on the ground or in tree hollows (Richards 1978). In a comprehensive study conducted by Gomes et al. (2007), they observed P. ignobilis foraging and preying on insects of the Diptera order found on pig carcass. Once captured and killed, these preys are reduced to a formless mass and subsequently distributed to nourish the brood (Gomes et al. 2007).

The stingless bees, Tetragonisca angustula (Latreille 1811) (Apidae: Meliponini), are eusocial bees with wide distribution in the Neotropical region (Nogueira Neto 1970). The society of this species is divided in castes: queen, workers, and guards (Baudier et al. 2019). Some of the guards stand in the nest entrance while others hover in front of the nest in a stable position, both to protect the nest against the attack from natural enemies (Kärcher and Ratnieks 2009). The presence of guards at the nest entrance may suggest successive clashes with natural enemies. For instance, they are known to defend the nest from the attack by the cleptobiotic Lestrimelitta limao (Apidae: Meliponini) by biting legs and wings of the cleptobiotic. According to Wittmann et al. (1990), the cephalic volatiles of L. limao have a kairomonal effect on T. angustula workers, as they trigger their defense behavior. It is worth mentioning that guards are also keen to recognize non-nestmates and defend the nest against drifting (Jones et al. 2012).

Despite the defensive behavior of T. angustula, we do not know how this species would defend their nests against natural enemies of bigger size known to be efficient wasp predators. We already know, in similar case, that the Asian hornet Vespa velutina can quickly strike and decapitate honey bees; however, outside the natural region of distribution, these bees did not yet develop efficient strategies for nest defense (Arca et al. 2014).

In this study, we present preliminary observations of attacks by the wasp P. ignobilis on the eusocial stingless bees, T. angustula at the nest entrance.

2 Material and methods

The observations were performed in a stingless bee nest placed at a beekeeping station, in the city of Itu, São Paulo, Brazil (23° 16′ S, 47° 15′ W). The beekeeping stations were about 14 m2 large with the presence of five nests of T. angustula and nests of several other wild bee species, such Centris (Apidae: Centridini), Xylocopa (Apidae: Xylocopini), and Euglossa (Apidae: Euglossini) species. The attacks by P. ignobilis always occurred on individuals from the same nest (Supplementary Figure S1), which was positioned in the corner of the bee station approximately 85, 245, 420, and 480 cm away from the other nests.

Occasional observations (n = 14) started when the wasp(s) were observed flying near the nest or already standing in the proximity of the nest and lasted until the wasp(s) dispersed. The records took place between 12:00 and 17:00 on 30th September and on 1st, 2nd, and 9th October 2023 on sunny days.

3 Results

During the preying attacks, the workers of P. ignobilis interrupted its flight by landing in nearby vegetation circa of 1.5 m from the nest entrance, or in the lateral of the T. angustula nest or directly on the wooden beam from which the nest was suspended only a few centimeters (~30 cm) from the nest entrance. In 85% (n = 12) of our observations, a single wasp was observed attempting to attack the bees. Only at two occasions, two wasps were simultaneously preying on bees. Before the attacks, it seemed that the wasps observed the behavior of the guard bees while hovering at the nest entrance. The wasp moved close to the nest entrance attempting to prey the bees while it was flying close to the nest entrance. Alternatively, the wasp started approaching the bees on foot walking on the hive wall. Following the latter, the wasps hub their antennae with the first two pairs of legs before moving towards the guard bees. The guard bees on the other hand flew in the direction of the wasp seeming to push the wasps away. Four different behavioral sequences of this attack/defense behavior were recorded: (1) A successful attack occurs when the wasp successfully preys on a bee (n = 10) and flew away carrying it (Supplementary Video 1a), (2) following unsuccessful attempts, the wasp eventually achieves successful preying (n = 2) (Figure 1), (3) an unsuccessful attack occurs when the wasp fails to prey on the bees (n = 1), and (4) an unsuccessful attack is followed by a guard bee attacking the wasp by biting its wing (n = 1) (Figures 2 and 3).

Figure 1.
figure 1

A P. ignobilis females handling a guard of stingless bee, T. angustula, after preying on it at the bee nest entrance (Photo: SB).

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Figure 2.
figure 2

A guard of T. angustula biting the left wing of a female of P. ignobilis near the stingless bee nest entrance (Photo: SB).

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Figure 3.
figure 3

Proportion of each behavior displayed by wasps and bees.

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4 Discussion

Previous reports suggest a generalist preying behavior of P. ignobilis (Gomes et al. 2007). The current observation introduces to the Neotropical region a not well-documented case of wasps killing bees at the nest entrance, similar to the classic case of V. velutina and the honey bees. Although P. ignobilis is probably more opportunistic than specialized in T. angustula, many questions need to be answered for a better understanding of this interaction. Here, we observed more often events which the wasps seem to have advantage in this agonistic interaction. Although we observed one event which the stingless bee guard counterattacked the wasps, we did not know if this ended efficiently since they were missed after falling on the grass surrounding the nest.

Polybia ignobilis is a generalist predator and, as other social wasp foragers, probably do not behave as eventual killers. They prey on several resource items, including caterpillars and adult insects. Previous studies reported their predation behavior on Diptera, Hemiptera, Hymenoptera, Coleoptera, and mainly Lepidoptera of several species (Gobbi and Machado 1986; Gomes et al. 2007). Although wasps preying on bees has not been deeply investigated (but see Koedam et al. 2009), it has been mentioned that members of the Kayapó indigenous tribe, in the Amazon forest, assigned two species of Polybia to enter the nest of stingless bees and steal honey (Camargo and Posey 1990). Certainly, it is worth continuing to study such interactions in the Neotropics and learn which are the mechanisms trigging these interactions and how they evolved. For instance, we did not observe a massive bee attack to the wasp, as seen in Asian honey bees defending against V. velutina. In the future, it would be interesting to study whether there is a chemical mechanism by which P. ignobilis locates this particular bee species and to investigate whether bees rely on visual, chemical, or a combination of sensory cues to detect the presence of the predator.

Although our observations reveal an interesting interaction at the nest entrance and show the consume of T. angustula guards by P. ignobilis as a protein source, several other questions remain. For instance, could the absence of a massive attack behavior by the bees have allowed for predation conditions on a small scale? What would happen whether the guards are killed by multiple attacks of the wasps, would this consequently lead to wasp invasion and steal of the honey, as observed by the Kayapó indigenous people reported earlier (Camargo and Posey 1990)? It would be interesting for researchers to connect to stingless beekeepers in the natural distribution range of T. angustula to gain more information in this interaction to clarify this predator-prey interaction and follow if this emerges as a potential threat to stingless bees in the future.