Hemipepsis ustulata

Hemipepsis ustulata

''Hemipepsis ustulata'' is a species of tarantula hawk native to the Southwestern United States. Tarantula hawks are a large, conspicuous family of long legged wasps which prey on tarantulas. They use their long legs to grapple with their tarantula prey before paralyzing them with a powerful sting. Their stings are ranked second most painful in the insect world. The tarantula hawk is also the state insect of New Mexico. They are a solitary wasp species, displaying lekking territorial behavior in their mating rituals.
A Tarantula Killer by Host This "spider wasp" is commonly referred to as the Tarantula Hawk. It seeks out by smell the largest spider of the Arizona desert the tarantulas. An incredible feat of attaching its larvae to the host which eventually devours it over the course of about 35 days until maturity. The host dies in the 5th instar. Hemipepsis ustulata,spider wasp,tarantula hawk

Appearance

''Hemipepsis ustulata'' generally have matte black bodies with rust-orange wings. They are among the largest of ''Hymenoptera'', growing up to 5 cm in length. It is difficult to distinguish ''Hemipepsis'' from their ''Pepsis'' relatives. However, ''Pepsis'' tend to be a more metallic black with a deep blue striped patterning. Since their biology and appearance is so similar, the only reliable way to tell them apart is by their wing venation patterns.
Tarantula hawk Tarantula hawk hanging around waiting for the Tarantula's to start getting active this summer. Desert,Geotagged,Hemipepsis ustulata,Pompilidae,Spring,Tarantula,Tarantula hawk,United States,spider wasp,wasp

Distribution

''Hemipepsis ustulata'' are common in the arid climate of Southwestern United States, ranging from California through Arizona, New Mexico, and Texas, and as far north as Nevada, Oklahoma, and Kansas. Much of the fieldwork done on ''Hemipepsis ustulata'' was performed in the Sonoran desert near Phoenix, Arizona by John Alcock. ''Hemipepsis ustulata'' distribution overlaps with therasphoid spiders, which they parasitize to raise their young.

Behavior

It is unknown how these wasps communicate with each other, especially within the aggregates they form. However, the powerful residual odors, flight patterns, and flashy colors are all likely for how they communicate with each other.Male ''Hemipepsis ustulata'' often pick palo verde trees as landmark territories. The most preferred territories tend to be located higher up the mountain ridges. During the male flight season, there is considerable turnover in territorial ownership. The average duration of male residence is around 8 days. Ownership is contested through aerial combat. Larger males have the advantage, displacing smaller males from the preferred territories over the course of the mating season. There is a great abundance of males during mating season; females are rarely seen. The operational sex ratio during this time is highly skewed towards males. In some ways, H. ustulata’s mating system resembles lek polygyny. In hilltopping insects, the male defends territories. Females may visit the territories, but they only remain long enough to mate, not to nest or feed. In a lekking species, the male-defended territory does not contain incentive of resources for females, such as food, shelter, or attractive nesting sites. Other characteristics of ''Hemipepsis ustulata''’s lekking behavior include: the existence of a mating arena, where males aggregate year after year, with each male protecting its own perch/display territory and receptive females mate selectively and upon the inspection of the territorial males.Oftentimes in the natural history of a species, large body size confers reproductive advantage. This raises the question in ''Hemipepsis ustulata'': why do smaller wasps persist? Generation after generation, there is a wide size variation among these tarantula hawks. Wasps do not grow after metamorphosis, so smaller animals are at a permanent disadvantage competing against their larger fellows. John Alcock’s studies emphasize the importance of size variation in claiming desirable territories among male ''Hemipepsis ustulata'' wasps. It is hypothesized that female provisioning behavior may play a role in the maintenance of size variation in this species. In tarantula hawks, the size of the offspring is determined by the mother’s decision on how much to invest in each offspring. The size of the tarantula captured by the mother wasp is a function of how big the larva will become when fully grown. The subduing of a larger tarantula requires a greater energy investment and poses a greater risk to the mother wasp. If the offspring is a large male, it would have to be twice as fit as a smaller male offspring in order to repay the investment of the mother wasp. Thus, in some cases, it may be advantageous for the mother wasp to produce many small male offspring. This would enable them to enjoy the same level of fitness as a female, but with fewer, larger progeny.

Habitat

''Hemipepsis ustulata'' are common in the arid climate of Southwestern United States, ranging from California through Arizona, New Mexico, and Texas, and as far north as Nevada, Oklahoma, and Kansas. Much of the fieldwork done on ''Hemipepsis ustulata'' was performed in the Sonoran desert near Phoenix, Arizona by John Alcock. ''Hemipepsis ustulata'' distribution overlaps with therasphoid spiders, which they parasitize to raise their young.

Reproduction

About three days after the egg is laid, the free end of the egg becomes glassy white. The grub chews its way out with its tiny dark-tipped mandibles. Eventually, the eggshell splits, revealing the glistening, white, footless grub. The grub, still attached to the host tarantula by its tail end, arches over and digs into the tarantula’s skin, creating a perforation aided by a dissolving fluid. Now that the grub is firmly attached by both its tail and head to the tarantula, it begins to suck the juices out of the tarantula’s body. As it feeds, the larva grows, rapidly engorging itself on the tarantula and darkening in color. As it grows, it molts several times, casting off its head capsule and body skin. After each molt, it resumes feeding, often through a new perforation. By the fourth instar, the tarantula’s abdomen has collapsed slightly. At the fifth and last instar, the larva has developed a pair of stout three-toothed mandibles in order to keep up with its feeding habits. The larva has become muscular and mobile by this stage. It will cut a hole into the tarantula’s carapace and thrust its head and thorax inside the host spider, continuing to feed ravenously. As it feeds, it hollows out the tarantula, up to the bases of the spider’s hairy legs. At the beginning of this invasive assault, the tarantula finally expires. This entire process from egg to fifth instar takes around 35 days total.The breeding season of ''Hemipepsis ustulata'' occurs over a two and a half month period. Individual males actively seek mates on mountain ridges for up to three weeks at a time. Many males live more than one month.

Food

''Hemipepsis ustulata'' larva feed on tarantulas that are paralyzed and captured by the adult wasp. Adult wasps spend lengthy periods of time patrolling, actively searching for prey on the ground. Adult wasps feed on nectar, and they visit flowers and flowering plants during the day. Popular sources of nectar include milkweeds and western soapberry trees .

Predators

The debilitating, painful sting of ''Hemipepsis ustulata'' deters nearly all predators. There are no known examples of amphibian, reptilian, or mammalian predation of adult tarantula hawks. The only documented examples of tarantula hawk predation are of kingbirds in Puerto Rico, discovered by a respected entomologist, Dr. Punzo, who observed two instances of roadrunners attacking grounded tarantula hawks. However, it is not known if those tarantula hawks were healthy at the time of attack, nor if they were male or female. As far as the literature goes, instances of predation by roadrunners are rare at best, even on harmless males, which speaks to the defensive effectiveness and reputation of tarantula hawks in the animal kingdom.

Defense

Territorial males of this species perch upon prominent vegetation at high elevation and chase intruders away. There is never more than one individual in each territory for more than a few minutes. Every so often, the landowning male wasp will make short regular flights out from its perch. Intruding visitors are common among this species, as males jockey for the best territory. On occasion, the intruder engages in aerial combat with the territory owner over possession of the perch, a tree or bush. The two males will clash wings and spiral vertically upwards engaging in an aerial contest for the territory.It is both biochemically and medically interesting how tarantula hawk venom works. How can an essentially non-toxic venom that causes so much pain, described as blinding, debilitating, and shockingly electric by Schmidt, subside in only three minutes in humans? Only the bullet ant is ranked higher than the tarantula hawk’s sting on Schmidt’s Sting Pain Index. How does it permanently paralyze a tarantula, yet keep it alive? It is also evolutionarily interesting and significant how such a toxin evolved. Selection pressure by potential vertebrate predators would have favored individuals with painful venom components, but not vertebrate-lethal components. At the same time, selection pressure against venom lethality towards prey and subsequent loss of prey to spoilage would be very strong. The tarantula hawk’s venom is a specific, evolutionarily tailored cocktail of compounds best suited to the wasps’ needs. Studying tarantula hawk venom may help us gain insight into treating human problems like chronic pain from injury or disease.

Evolution

Oftentimes in the natural history of a species, large body size confers reproductive advantage. This raises the question in ''Hemipepsis ustulata'': why do smaller wasps persist? Generation after generation, there is a wide size variation among these tarantula hawks. Wasps do not grow after metamorphosis, so smaller animals are at a permanent disadvantage competing against their larger fellows. John Alcock’s studies emphasize the importance of size variation in claiming desirable territories among male ''Hemipepsis ustulata'' wasps. It is hypothesized that female provisioning behavior may play a role in the maintenance of size variation in this species. In tarantula hawks, the size of the offspring is determined by the mother’s decision on how much to invest in each offspring. The size of the tarantula captured by the mother wasp is a function of how big the larva will become when fully grown. The subduing of a larger tarantula requires a greater energy investment and poses a greater risk to the mother wasp. If the offspring is a large male, it would have to be twice as fit as a smaller male offspring in order to repay the investment of the mother wasp. Thus, in some cases, it may be advantageous for the mother wasp to produce many small male offspring. This would enable them to enjoy the same level of fitness as a female, but with fewer, larger progeny.Evidence suggests the convergent evolution in perching and patrolling site preferences of ''Hemipepsis ustulata'' with other hilltopping insects of the Sonoran Desert. The high mountain ridges attract the males of various hilltopping insect species, including tarantula hawk wasps, various butterflies, and bot flies. Among these ridges, certain locations are much more likely to be occupied by territorial males. Additionally, these preferred territories appear to be stable from year to year, and different species appear to have similar preferences for available sites. Preferred territories tend to be large, visual targets, jutting high on mountain ridges. These observations were confirmed by a study using artificial landmarks. This similar ranking preference for territories suggests a widespread convergence among the capacity of hilltopping insects’ compound eyes in their perception of what constitutes a conspicuous landmark feature.

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Taxonomy
KingdomAnimalia
DivisionArthropoda
ClassInsecta
OrderHymenoptera
FamilyPompilidae
GenusHemipepsis
SpeciesH. ustulata