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The Tarantula Hawk
By: Stephen Potter
Classification:
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Hymenoptera
Suborder: Apocrita
Family: Pompilidae
Subfamily: Pepsinae
Genus: Pepsis
Figure 1. Tarantula Hawk Pepsis Grossa
Description
Wasps that belong to the family Pompilidae are referred to as spider wasps. Spider wasps will target different species of spiders (depending on the species of spider wasp), paralyze them, and use the living spider as a host for the wasp larvae to grow in. Tarantula hawks are species of spider wasps belonging to the genus Pepsis that, as the common name implies, attack theraphosid spiders that are several times larger than themselves (Schmidt 2004). Both male and female spiders are attacked, either in their burrows or free ranging, and stung with rapid and complete paralysis (Schmidt 2004). The tarantula hawk does not feed off the paralyzed spiders. The larvae will consume the spider once they hatch, but the adult tarantula hawk is commonly seen feeding on nectar from different nectar sources.
The tarantula hawk species Pepsis grossa is one of the several species of these spider wasps that are found the southwestern deserts of the United States. This species is the largest that will be found in the United States with body length of males being from 23 to 40 millimeters and the body length of females being from 30 to 51 millimeters. Pepsis grossa experience aposematism, warning coloration, which prevents potential predators from getting too close. Both male and females are observed in a xanthic and melanic form in the United States with metallic black or blue-black bodies and often either bright yellow-orange or iridescent black wings (Schmidt 2004). These are common warning colors that can be seen in other animals such as poisonous frogs, reptiles, and other insects.
Figure 2. Pepsis wasp
Distribution
There are many species of tarantula hawks in the genus Pepsis that can be found across the world, mostly in warmer climates. Tarantula hawks have been observed in India, Southeast Asia, Australia, Africa, and both of the Americas. Tarantula hawks are solitary creatures that are commonly seen by themselves. Occasionally they are seen in groups aggregating around nectar sources. In the United States, tarantula hawks are common in the southwestern deserts of the country, but they have been found as far north as Washington. The species Pepsis grossa is one of the many species of tarantula hawks that can be found in the south western deserts of the United States. In 1989, the state of New Mexico chose the Tarantula Hawk (Pepsis grossa) as the official state insect.
Figure 3. Pepsis distribution globally.
Sting
Figure 4 refers to a pain scale called the Schmidt Insect Sting Pain Index. Insects that are ranked in this scale are from the order Hymenoptera, which include wasps, bees, and ants. The index was created by entomologist Justin Schmidt in order to scale the pain received from various Hymenoptera bites/ stings. The index is scaled from 1 to 4, 1 being your common bee sting or fire ant bite to 4, being next to unbearable pain. The Tarantula Hawk, including the species Pepsis grossa, is ranked as a four next to the Bullet Ant, Paraponera clavata, for being the most painful sting/ bite known from all insects. The pain from a Tarantula Hawk sting has been described as instantaneous, electrifying, excruciating, and totally debilitating (Schmidt 2004). Advice given from Schmidt to anyone who has been stung by a Tarantula Hawk is to “lay down and scream”. There is a certain threshold for pain where you are unable to maintain total cognitive control. He says to lie down and scream so when you are stung you do not try and run, possibly injuring yourself by falling or running into a cactus or a fence. The good news for those stung is that the pain usually decreases to a minor level after about 3 minutes and is gone shortly thereafter, leaving the person emotionally and physically drained (Schmidt 2004). An example of an incident involving tarantula hawks, as explained by Schmidt, involved an entomologist named Howard Evans. Howard Evans netted perhaps 10 tarantula hawk females from a flower and enthusiastically reached into the insect net to retrieve them. Undeterred after the first sting, he continued, receiving several more stings, until the pain was so great he lost all of them and crawled into a ditch and just bawled his eyes out (Schmidt 2004).
Figure 4. the Schmidt Insect Sting Pain Index
The venom from Pepsis grossa is an instant paralytic poison for arachnids and other insects that are stung, but to mammals it has no effect. The non-toxic venom also has one or more unidentified components that quickly target the neuromuscular junctions of the spider, deeply paralyzing it (Schmidt 2004). At best, tarantula hawk venom is only about 5% as lethal as that of honey bees or the yellow-jacket wasp Vespula squamosa , 2% that of a bullet ant, and 0.2% that of a harvester ant (Schmidt 2004). The venom that would cause instant and total paralysis in a tarantula or any other spider would only react with skin tissue of mammals and cause brief, excruciating pain. To test this, Wasps were collected in Southern Arizona, usually while foraging or aggregating on nectar sources, placed in sealed approximately 250–500 ml jars, and immediately chilled on crushed ice. Upon return to the laboratory, the cold immobilized wasps were frozen and maintained at −24°C until venom collection (Schimdt 2004). When the venom of the Pepsis wasps were injected intravenously into small lab mammals, there was little or no effect on the mammal. Along with their aposematism, the pain of a Tarantula Hawk’s sting is enough to ensure that they are not bothered by birds or other mammals that may usually feed on insects.
Search Behavior/ Larva interaction with tarantula
Tarantula Hawks have been witnessed as very active when it comes to searching for a host when they are ready to produce offspring. It can be a tedious matter to observe any species of Tarantula hawk search for tarantulas and observe them laying their egg on the theraphosid. To further complicate matters, spider wasps, unlike many digger wasps, are not very gregarious and often construct burrows near their hunting grounds (Kurczewski 1973). Most species make only a single-celled, shallow nest, stock it with one spider, and go elsewhere to construct their next nest (Kurczewski 1973). The method of attack on a theraphosid is a very interesting one to observe. A female Tarantula Hawk will find a tarantula by smell. It is hypothesized that the female Tarantula hawk can find a tarantula burrow by the smell of the webbing used to create the entrance to the burrow. The female will then draw the spider out, sometimes by entering the spider burrow. In the encounters with tarantulas up to several times larger than the wasp, no wasp deaths in 200 encounters were recorded (Schmidt 2004). The female will use their mandibles to grab on of the front tarantula legs and flip the spider over, exposing its vulnerable belly. It takes its prey by stinging, thus instantly paralyzing every limb of its victim (Lincecum 1867). The paralysis is permanent and the host is dragged, sometimes more than several meters, to either the tarantula’s burrow or a burrow made by the wasp, where the egg will be laid on the spider. If a paralyzed tarantula dies before being consumed by a wasp larva, the larva dies (Williams 1956). The larva will feed on the tarantula, leaving major circulatory systems for last, until the spider is dead.
Figure 5. Tarantula Hawk dragging a tarantula.
Hill-topping
An interesting behavior seen by some species of male tarantula hawks in a mating ritual called hill-topping. Hill-topping is seen by different species of butterflies, dragonflies, wasps, and beetles. Male tarantula hawks will fly to peak tops where receptive females of their species will sometimes appear (Alcock 2008). Hilltopping males guard entire shrubs or trees where they perch and wait for inincoming virgin females (Alcock 2008). In a study performed by John Alcock, they wanted to determine how long a male Tarantula hawks would stay in their territory. The study was conducted primarily during March-June 2006 and 2007 at Usery Mountain, Maricopa Co., Arizona, on the highest part of the mountain at an elevation of 900 m, which had typical upland vegetation (Alcock 2008). The site was visited 51 days in 2006 and 32 days in 2007. They would capture and mark the male tarantula hawks, mark them, and then return a number of days later to observe if the male tarantula hawks around these plants were marked or not. What he found was the mean time a male would stay to wait for a female was 17.0 days in 2006 and 15.1 days in 2007, with the difference between the two values not being significant (t 5 0.75; df 5 15; P . 0.05) (Alcock 2008).
Works Cited
Alcock, J. (2008). Territorial preferences of the hilltopping wasp Hemipepsis ustulata (Pompilidae) remain stable from year to year. The Southwestern Naturalist, 53(2), 190-195.
Kurczewski, F. E., & Kurczewski, E. J.. (1973). Host Records for Some North American Pompilidae (Hymenoptera). Third Supplement. Tribe Pompilini. Journal of the Kansas Entomological Society, 46(1), 65–81. Retrieved from http://www.jstor.org/stable/25082547
Lincecum, G.. (1867). The Tarantula Killers of Texas. The American Naturalist, 1(3), 137–141. Retrieved from http://www.jstor.org/stable/2449695
Schmidt, J. O. (2004). Venom and the good life in tarantula hawks (Hymenoptera: Pompilidae): how to eat, not be eaten, and live long. Journal of the Kansas Entomological Society, 77(4), 402-413.
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