The indestructible insect: Velvet ants from across the United States avoid predation by representatives from all major tetrapod clades

Abstract

Velvet ants are a group of parasitic wasps that are well known for a suite of defensive adaptations including bright coloration and a formidable sting. While these adaptations are presumed to function in antipredator defense, observations between potential predators and this group are lacking. We conducted a series of experiments to determine the risk of velvet ants to a host of potential predators including amphibians, reptiles, birds, and small mammals. Velvet ants from across the United States were tested with predator's representative of the velvet ants native range. All interactions between lizards, free‐ranging birds, and a mole resulted in the velvet ants survival, and ultimate avoidance by the predator. Two shrews did injure a velvet ant, but this occurred only after multiple failed attacks. The only predator to successfully consume a velvet ant was a single American toad (Anaxyrus americanus). These results indicate that the suite of defenses possessed by velvet ants, including aposematic coloration, stridulations, a chemical alarm signal, a hard exoskeleton, and powerful sting are effective defenses against potential predators. Female velvet ants appear to be nearly impervious to predation by many species whose diet is heavily derived of invertebrate prey.

Stinging wasps (Hymenoptera: Aculeata), which species have the longest sting?

“…First, as is mentioned above, the length and agility of the sting, combined with their extraordinarily hard cuticle, aposematic coloration, and stridulation enables velvet ants to quickly and effectively train predators to avoid them. Gall et al (in press) , for example, found that when a lizard (in this study the lizard was Aspidoscelis tigris ) attacks a velvet ant, it is unable to crush it because of the hard cuticle, as the lizard attempts to manipulate the velvet ant in its mouth, the velvet ant is quickly able to sting the lizard. Once released, the aposematic coloration of the velvet ant apparently facilitates rapid learning in the lizard.…”

“…Velvet ants, on the other hand, parasitize hosts (immature hymenoptera) that are already immobile, and it has been suggested that their sting and associated venom is primarily used for defense ( Schmidt, 2016 ). Highly toxic venom for defense might be selected against, as it would be more beneficial for a velvet ant to inflict pain, but not mortally wound a potential predator facilitating learned avoidance, which has been demonstrated in feeding trials with various vertebrates ( Gall et al, in press ).…”

“…Once released, the aposematic coloration of the velvet ant apparently facilitates rapid learning in the lizard. In many instances after experiencing the sting of a velvet ant (and the other defenses) a lizard will not attempt to attack another velvet ant, even with over a year between exposures to these wasps ( Gall et al, in press ). The second aspect of velvet ant stings and venom chemistry that make them highly effective predatory deterrents is the mildly toxic, but highly painful sting.…”

Predators as drivers of insect defenses

“…Thus, a more comprehensive study would include multiple predator types. In the few such studies to date, no universal antipredator defenses have been found (Honma et al 2006;Gall et al 2018). Furthermore, antipredator defenses can vary intraspecifically.…”

Defensive Venoms: Is Pain Sufficient for Predator Deterrence?

“…Surprisingly, given their presumed importance, defensive venoms have been poorly studied [20,22,38]. Only a handful of investigations have demonstrated the efficacy of such venoms against natural predators [21,[38][39][40][41][42][43]. Moreover, no study has attempted to tease apart the relative contributions of the painful vs. toxic elements to a venom's effectiveness in deterring an enemy, perhaps because most defensive cocktails contain both components [23].…”