Let’s return to Volcán del Toro to learn more about the defenses of the two-spotted tiger beetle, Pseudoxycheila tarsalis. In last week’s episode we discovered its special powers of speed and chemical defense, survival strategies for the rainforests of Costa Rica. Along the same winding trail where we met the two-spotted tiger beetle, we encountered a remarkable velvet ant dashing across the path. This handsome creature, likely a member of the genus Pseudomethoca, bore two large white patches on its jet-black abdomen, the tip of which was encircled with white bars. A topnotch of golden hair flashed in the sunlight as it bustled across the ground.
Female velvet ants boldly search for galleries of ground nesting bees in which to deposit their eggs. A wicked sting provides a potent defense for the female velvet ant.
Velvet ants are not ants at all. Ants are social insects ruled by one or more queens governing a caste system of workers. Velvet ants are wasps in the family Mutillidae, a large group of solitary wasps that prey upon ground-nesting bees. Wingless female velvet ants roam the earth in search of nests of solitary or social bees. Upon discovering a nest, they deposit eggs within, eggs that soon hatch into rapacious larvae that devour the brood of ground-nesting bees. The name velvet ant derives from the coat of fine hairs adorning their bodies. This cloak is often brightly colored with contrasting patterns of black, red, orange, yellow, or white. Velvet ants are not trying to blend in with their surroundings, just the opposite, they are trying to stand out. Here is why. Velvet ants have the reputation of possessing one of the fiercest stings in the entire realm of insects, so much so, that one large red and black resident of North America goes by the name of “cow killer.” We met this gorgeous insect in a previous episode of Bug of the Week. Bright contrasting colors and bold diurnal activity are believed to warn would-be predators of a wicked sting should they decide to attack a female velvet ant. Following the first encounter with a velvet ant, a visually hunting predator may have learned to associate the characteristic color pattern of the velvet ant with its wicked sting and eschew an attempt of a second attack.
Stinging velvet ant and chemically defended beetle. Do the white spots tell predators “don’t mess with me?”
And herein lies the third special power of the two-spotted tiger beetle. Scientists believe that the two white spots on the wing covers of the tiger beetle resemble the two white spots on the abdomen of the velvet ant, thereby sending a warning to a would-be predator that an attack may have unpleasant consequences. This visual warning may help reinforce the potent chemical defense of the tiger beetle discussed in the last episode. The phenomenon of developing an easily recognizable color pattern by two or more insects with potent defenses is called Müllerian mimicry, so named for the visionary German naturalist Fritz Müller. Velvet ants and tiger beetles are just two of the charismatic members of the rich web of life found in the tropical rainforest.
Bug of the Week thanks Orlando for inspiring this episode and Dr. Shrewsbury for providing the image of the two-spotted tiger beetle. “Tiger beetle defenses revisited: Alternative defense strategies and colorations of two neotropical tiger beetles, Odontocheila nicaraguensis Bates and Pseudoxycheila tasalis Bates (Carabidae : Cicindelinae)” by Tom D. Schultz was consulted for this episode.