Tarantula hawks, belonging to the genera Pepsis and Hemipepsis, are a fascinating group of spider wasps renowned for their unique hunting behavior and vibrant coloration. These wasps, found across diverse habitats from the Mediterranean to the Americas, have evolved a specialized predatory strategy focused on tarantulas. This article explores the tarantula hawk's diet, hunting techniques, and ecological significance.
Identifying Tarantula Hawks
Tarantula hawks are easily recognizable due to their striking appearance. These parasitoid wasps are among the largest of wasps, growing up to 6.5 centimeters (2+1⁄2 in) long. They exhibit aposematism through their vivid coloration, featuring blue-black bodies and bright, rust-colored wings, though some species have black wings with blue highlights. This serves as a warning to potential predators about their potent sting. Their long legs are equipped with hooked claws, essential for grappling with their tarantula prey. The males have straight antennae and the females are curled.
Distribution and Habitat
Tarantula hawks have a wide distribution, inhabiting regions from the Mediterranean basin to Southeast Asia, Africa, Australia, and the Americas. Within the New World, the genus Pepsis is exclusively found, with species ranging from as far north as Logan, Utah, to Argentina. At least 250 species reside in South America. In the United States, 18 species of Pepsis and three species of Hemipepsis are present, primarily in the deserts of the Southwestern United States. Common species include Pepsis grossa (formerly P. formosa) and Pepsis thisbe. These wasps typically inhabit shrub lands, grasslands, and arroyos.
The Hunting Process: A Deadly Encounter
The most remarkable aspect of the tarantula hawk's life cycle is its hunting behavior. The female tarantula hawk is the primary hunter, while the male does not participate in hunting activities. When a female tarantula hawk is ready to reproduce, she embarks on a hunt for a suitable tarantula. This may involve locating a roaming male tarantula or finding a tarantula's burrow. Adult males leave their burrows in search of female tarantulas. In Bandelier, they are rarely seen except in autumn (mostly October). The journey can be long, arduous, and deadly. Many tarantulas are run over by cars as they cross roadways or are eaten by predators before they ever find a partner. The female tarantula hawk searches for tarantulas by smell.
Luring the Tarantula
Upon locating a burrow, the female wasp attempts to lure the tarantula out. She may tap and strum webbing at the burrow entrance, imitating prey to draw out the spider. Sometimes she locates a tarantula burrow and tugs at the sensitive silk strands surrounding the den, imitating prey to draw out the spider. When the male tarantula detects a female, he cautiously approaches the entrance to the female's burrow. Once at the entrance he taps his foot to alert the female to his presence. If the female is receptive, she cautiously emerges from her den. If the female tarantula is hungry or has already mated, she is just as likely to make the male tarantula her next meal as she is to make him her mate.
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The Sting and Paralysis
If the tarantula responds, a potentially lengthy battle ensues. More often than not, the tarantula hawk emerges victorious, delivering a paralyzing sting to the tarantula. The female tarantula hawk stings a tarantula between the legs, paralyzing it. The wasp darts under the tarantula and bites a hind leg while using its own hind legs to hold the tarantula’s fangs out of biting range. The venom injected by the wasp is potent, rendering the tarantula almost instantly paralyzed. Although chances for survival are slim, all hope is not lost for the tarantula. In at least one species, if the wasp egg does not hatch, the venom will eventually wear off, allowing the tarantula to make a full recovery.
Transport and Oviposition
Once the tarantula is immobilized, the female wasp drags the prey to a specially prepared burrow. This can be a considerable distance, even over downed trees and large rocks. Unable to resist, the tarantula is dragged to a pre-dug burrow and dropped in. She will next deposit eggs on the tarantula. The tarantula hawk then lays her eggs on the still-living tarantula and leaves, covering the den's entrance. The female lays just one egg on the abdomen of the paralyzed spider. Sex of offspring is determined by fertilization; fertilized eggs produce females, while unfertilized eggs produce males.
Larval Development: A Gruesome Feast
The reproductive cycle of the tarantula hawk wasp is an intricately designed sequence that guarantees the continuation of its progeny. This begins as adult tarantula hawks participate in courtship, which leads to the female seeking out a living space within a captured tarantula for her offspring - essentially using it as an incubator for her egg. The grub-like larva feed on the tarantula. In a span of three to four days, the egg gives way to a small larva. This newborn larva starts feeding on its live tarantula host right away, methodically devouring it in order to sustain itself and grow. When the wasp larva hatches, it creates a small hole in the spider's abdomen, then enters and feeds voraciously, avoiding vital organs for as long as possible to keep the spider alive. After several weeks, the larva pupates and go into a resting stage. After consuming the tarantula, the larva pupates (just like a caterpillar making a cocoon) and emerges as an adult wasp.
Adult Diet and Behavior
Adult tarantula hawks are nectarivorous, meaning they primarily feed on nectar from flowers. During the day they spend most of their time feeding around flowers. They are notable pollinators, primarily attracted to the nectar found in a wide array of plants they visit. While adult tarantula hawks consume nectar, it’s only the females that pursue and capture spiders for their offspring’s nourishment. The plants they visit. Both males and females feed on the flowers of milkweeds, western soapberry trees, or mesquite trees. Male tarantula hawks have been observed practicing a behavior called hill-topping, in which they sit atop tall plants and watch for passing females ready to reproduce.
The Tarantula Hawk Sting: Painful but Not Deadly
The tarantula hawk is famous for its incredibly painful sting. On the Schmidt Pain Index, the tarantula hawk’s sting ranks just below the infamous bullet ant, making it one of the most painful stings known to humans. Entomologist Justin Schmidt, who subjected himself to insects stings in the name of science (and possibly masochistic tendencies) described the pain as “immediate, excruciating pain that simply shuts down one's ability to do anything, except perhaps scream. Schmidt has described the pain of the tarantula-hawk wasp as “immediate, intense, excruciating, and totally debilitating. The pain is so debilitating and excruciating that few, if any, can maintain normal coordination or cognitive control” if stung. The tarantula hawk’s sting is rated as a “4” on the Schmidt Sting Pain Index. The index ranges from 1 to 4 and a “4” is described by Schmidt as “blinding, fierce, shockingly electric. One researcher described the pain as "…immediate, excruciating, unrelenting pain that simply shuts down one's ability to do anything, except scream. Mental discipline simply does not work in these situations." Despite the intense pain, the sting is not considered lethal to humans and does not necessitate medical intervention. Aside from the possibility of triggering an allergic reaction, the sting is not dangerous and does not require medical attention. The pain completely subsides after a few minutes, leaving no permanent damage.
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Ecological Role and Conservation
Tarantula hawks are instrumental in ecological equilibrium, serving not only as pollinators but also as regulators of tarantula numbers. Tarantula hawk wasps are integral in controlling the population of spiders, especially tarantulas, aiding in the prevention of their overabundance and sustaining a balanced ecosystem.
Tarantula Hawks and Humans
Despite their formidable reputation, tarantula hawks are actually quite docile when unprovoked. They don’t show unprovoked aggression toward humans. Their bold coloration and charismatic swagger make tarantula-hawk wasps an entertaining and welcome addition to the Texas landscape.
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