Pepsis grossa
| Pepsis grossa | |
|---|---|
 | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Class: | Insecta |
| Order: | Hymenoptera |
| Superfamily: | Pompiloidea |
| Family: | Pompilidae |
| Subfamily: | Pepsinae |
| Tribe: | Pepsini |
| Genus: | Pepsis |
| Species: | P. grossa |
| Binomial name | |
| Pepsis grossa (Fabricius, 1798)[1] | |
| Synonyms[1] | |
| |
Pepsis grossa, formerly and perhaps better known as Pepsis formosa,[1] is a very large species of pepsid spider wasp from the southern part of North America, south to northern South America. It preys on tarantula spiders, giving rise to the name tarantula hawk for the wasps in the genus Pepsis and the related Hemipepsis. Only the females hunt so only they are capable of delivering a sting, which with that of the bullet ant is considered the most painful of any insect sting scoring 4.0 to the bullet ant's 4.0+ on the Schmidt sting pain index.[2] It is the state insect of New Mexico.[3] There are three colour morphs, the xanthic orange winged form and the melanic black winged form. In northern South America there is a third form, known as "lygamorphic" which has a dark base to the wings which have dark amber median patches and a pale tip.[4]
Description
A very large wasp which has three colour forms, an orange-winged (xanthic) form, a black-winged (melanic) form and a form which shows a three coloured wing pattern. The three colour forms are normally geographically separated, the melanic form occurs in the western part of the North American range, the xanthic form predominates over the remainder of the distribution except that lygamorphic individuals predominate in the southernmost part of the species range. Individuals of the melanic form of P. grossa are difficult to separate from Pepsis mexicana, but P. mexicana is always noticeably smaller than P. grossa.[5] The females body length is between 30-51mm, the males 24-40mm.[4] The black and orange colour pattern combine with the wasps jerky behaviour and strong odour to give a aposemastic warning to predators.[6]
Male Pepsis grossa are distinct within the genus Pepsis in that they have only 12 antennal segments, a scape, a pedicel, and 10 flagellomeres). The males of all other Pepsis species possess 13 antennal segments (i.e. 11 flagellomeres).[5] Fresh female P.grossa have long coarse hairs beneath the femur of the front leg but these can be worn off in older specimens.[4]
Biology
These wasps prey almost exclusively on tarantulas of the family Theraphosidae and the main species preyed upon by P. grossa is Aphonopelma hentzi.[7] The female wasps hunt in a crepuscular pattern, avoiding the intense daytime sun, by flying low over the ground, detecting their prey using vision or scent, possibly detecting the occupied burrows by the scent of the silk curtain the spider weaves over the entrance. The females may also hunt on the substrate, flicking her wings and antennae quite intensively.[4]
Once a spider has been detected the wasp uses its mandibles and carefully enters the spider's burrow. This seems to cause the spider to leave the burrow where it and the wasp can fight, the wasp has to evict the spider to ensure it has space to manoeuvre. Once the spider has been evicted the wasp steps away from it and grooms itself before using its antennae to cause the spider to raise itself into a threat posture by raising its front legs and baring its fangs. The wasp then grabs the second legs and injects the spider with its sting between the base of the leg and the sternum, striking a nerve centre and causing paralysis in the spider. She may then feed on fluid exuding from the wound she has caused or she may groom herself again. The wasp may then drag the spider back into its burrow, or she may dig a new burrow, before laying a single egg on the spider and sealing the burrow.[4]
The larva hatches from the egg and carefully consumes the paralysed spider and when it is finished consuming the spider’s vital organs, the larva weaves a silken cocoon for itself, It then metamorphoses into a pupa before emerging as an adult wasp.[8] When the female is choosing spiders she selects the larger specimens, usually females, to lay fertilised eggs on and these produce female wasps, unfertilised eggs are laid on captured male spiders and these hatch into male wasps.[6]
In Big Bend Ranch State Park, Texas, four species of plant accounted for 73.6% of all plants which were used by P, grossa adults for feeding on, these were the milkweeds: Ascepias texana and Ascepias sperryi; Mexican buckeye Ungnadia specisosa and honey mesquite Prosopis glandulosa[9] Wasps of the genus Pepsis do seem to be important pollinators of milkweeds which are regarded as noxious weeds as they are poisonous to grazing livestock.[7]
P. grossa form mixed-species, mixed sex aggregations that appear to be defensive in nature and probably assist in the location of resources and mating opportunities.[10]
Predators
These wasps are infrequently recorded as prey for other animals with kingbirds Tyrannus spp and the greater roadrunner Geococcyx californianus being recorded as preying on P. grossa. The roadrunner beat the wasp against the ground before it ate it.[7] Roadrunners have also been known to kleptoparasitise tarantula hawks, i.e. steal the spider from the wasp while otherwise leaving the wasp unharmed.[6] The American bullfrog Lithobates catesbeianus has also been recorded preying on these wasps.[11]
Mimics
The robber fly Wyliea mydas is a batesian mimic of both Pepsis grossa and Pepsis thisbe by having a black body and bright orange wings and by making stinging motions, exposing genitalia at the tip of its abdomen as if they were a sting.[12] Other Batesian mimics include the fly Mydas xanthopterus[13] as well as other Diptera, Coleoptera, moths, acridid grasshoppers, and other Hymenoptera.[10]
Distribution
From the southern United States of America as far north as Kansas through Mexico and Central America south to northern South America, including the islands of the Caribbean.[4]
Sting
Wasps of the genera Pepsis and Hemipepsis produce large quantities of venom and when stung humans experience immediate, intense, excruciating short term pain. Although the immediate pain of a tarantula hawk sting is among the greatest recorded for any stinging insect, the venom itself is not very toxic. The lethality of 65 mg/kg in mice for the venom of P. formosa pattoni reveals that the defensive value of the sting and the venom is based entirely upon pain. The pain experienced by the potential predator also forms an enabling basis for the evolution of aposematic coloration, aposematic odor, and a Müllerian mimicry complex involving most species of tarantula hawks as well as Batesian mimicry with other harmless insect species.[10]
New Mexico State Insect
A ballot to select a state insect for New Mexico was returned by almost 10,000 fourth, fifth, and sixth graders from 100 New Mexico Schools and the tarantula hawk wasp was chosen by an overwhelming margin, receiving over 50% of the vote. Following which, on 3 April 1989, New Mexico Governor Garrey Carruthers signed House Bill No. 468 declaring that the tarantula hawk wasp Pepsis formosa was the official insect of the State of New Mexico.[14]
Taxonomic Notes
Until 2002 P. grossa was known by the name Pepsis formosa, but C.R. Vardy synonymized P. formosa into P. grossa.[5]
References
- 1 2 3 "Species details : Pepsis grossa (Fabricius, 1798)". ITIS. Retrieved 10 September 2016.
- ↑ "Schmidt Pain Index (Which Sting Hurts the Worst?)". ScienceBlogs LLC. Retrieved 10 September 2016.
- ↑ "Tarantula Hawk Wasp New Mexico State Insect". State Symbols USA. Retrieved 10 September 2016.
- 1 2 3 4 5 6 "Wasp Wednesday Pepsis grossa". Eric R. Eaton. Retrieved 10 September 2016.
- 1 2 3 "Species Pepsis grossa". Iowa State University. Retrieved 10 September 2016.
- 1 2 3 "Instantaneous, Electrifying, Excruciating Pain The life history of the tarantula hawk is similar to that of many other solitary wasps. Its sting, however, is not.". Justin O. Schmidt. Retrieved 10 September 2016.
- 1 2 3 Vardy, C.R. (2000). "The New World tarantula-hawk wasp genus Pepsis Fabricius (Hymenoptera: Pompilidae). Part 1. Introduction and the P. rubra species-group". Zool. Verh. Leiden. 332 (29.xii): 1–86.
- ↑ "The enticing Tarantula Hawk". wordpress.com. Retrieved 10 September 2016.
- ↑ Punzo, Fred (2006). "Plants Whose Flowers Are Utilized by Adults of Pepsis Grossa Fabricius (Hymenoptera: Pompilidae) as a Source of Nectar". Journal of Hymenoptera Research. 15 (1).
- 1 2 3 Schmidt, Justin 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.
- ↑ "Tarantula Hawk". blogspot.co.uk. Retrieved 11 September 2016.
- ↑ "A Born Mimic: Toxic Robber Fly Mimics Tarantula Hawk Wasp". American Museum of Natural History. Retrieved 10 September 2016.
- ↑ "Tarantula Hawk – Big Sting". DFW Urban Wildlife. Retrieved 11 September 2016.
- ↑ "New Mexico Sate Insect". NSTATE, LLC. Retrieved 11 September 2016.