| Velvet ant | |
|---|---|
 | |
| Dasymutilla spp. | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Class: | Insecta |
| Order: | Hymenoptera |
| Superfamily: | Pompiloidea |
| Family: | Mutillidae Latreille, 1802 |
| Subfamilies | |
Mutillinae | |
Velvet ants (Mutillidae) are afamily of more than 7,000 species ofwasps whose winglessfemales resemble large, hairyants. Theircommon name velvet ant refers to their resemblance to anant, and their dense pile of hair, which most often is bright scarlet or orange, but may also be black, white, silver, or gold. Their bright colors serve asaposematic signals. They are known for their extremely painfulstings, (the sting of the speciesDasymutilla klugii rated a 3 on theSchmidt pain index and lasts up to 30 minutes[1]), and has resulted in the common name "cow killer" or "cow ant" being applied to the speciesDasymutilla occidentalis.[2] However, mutillids are not aggressive and sting only in defense. In addition, the actual toxicity of their venom is much lower than that of honey bees orharvester ants.[3] Unlike trueants, they are solitary, and lack complex social systems.[4]
Mutillidae can be found worldwide with about 230 genera or subgenera and around 8,000 species worldwide. Over 400 species occur in the North American Southwest.[5]
North American Mutillidae have eight phenotypically distinct and geographically limitedMüllerian mimicry rings (Desert, Eastern, Madrean, Texan, Red-headedTimulla, Black-headedTimulla, Tropical, and Western) making up one of the largest Müllerian mimicry complexes on the planet.[6] These mimicry rings are the result of repeated convergent evolution of aposematic traits between co-occurring velvet ant species, rather than shared phylogenetic history.[7] Through the evolution ofaposematic traits in velvet ant species in the same ring, local predators have learned to avoid these well-defended wasps.
Theexoskeleton of all velvet ants is unusually tough (to the point that some entomologists have reported difficulty piercing them with steel pins when attempting to mount them for display in cabinets).[citation needed] This characteristic allows them to successfully invade the nests of their prey and also helps them retain moisture. Mutillids exhibit extremesexual dimorphism. As in some related families in theVespoidea, males have wings, but females are wingless. The males and females are so distinct in theirmorphology that entomologists often find it very hard to determine whether a given male and female belong to the same species, unless they are captured while mating.[8] In some species, the male carries the smaller female aloft while mating, which is also seen in the related familyThynnidae.
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As is the case for allaculeates, only female mutillids are capable of inflicting a sting. The stinger is a modified female organ called anovipositor, which is unusually long and maneuverable in mutillids. In both sexes, a structure called astridulitrum on themetasoma is used to produce a squeaking or chirping sound when alarmed. Both sexes of mutillids also bear hair-lined grooves on the side of themetasoma called felt lines. Only two other vespoid families (Bradynobaenidae andChyphotidae) have felt lines, but the females of these families have a distinctpronotum, with a transverse suture separating it from themesonotum; in female mutillids, these two thoracic segments are completely fused. Members of the familyMyrmosidae, formerly classified as a subfamily of mutillids, also have a distinct pronotum in females, but lack felt lines in both sexes.
Adult mutillids feed onnectar. Although some species are strictly nocturnal, females are often active during the day. Females ofTricholabiodes thisbe are sometimes active up to two hours before sunset. Guido Nonveiller (1963) hypothesized the Mutillidae are generallystenothermic andthermophilic; they may not avoid light, but rather are active during temperatures that usually occur only after sunset.
Predation is one of the strongest forces natural selection uses to drive the evolution of an organism's morphology, physiology, and behavior.[9][10][11] During this coevolution, the prey either being consumed by the predator or escaping has resulted in a plethora of impressive defensive strategies in prey species to improve the likelihood of escape. Velvet ants avoid predation using the following defense mechanisms: a venomous sting (if female),aposematic coloration, astridulatory organ in their abdomen, an alarm secretion from their mandibular gland, and a durable exoskeleton. This array of defenses has contributed to the velvet ants being attributed the title of "the indestructible insect." This title was bestowed on them after experimental interactions between velvet ants and their potential predators that resulted in the survival of the ant and the ultimate avoidance by the predator.[12]
The venom that velvet ants inject through their stinger has been investigated for five species ofDasymutilla, revealing that they are composed primarily of peptides.[13] According to one researcher, the painfulness of the sting ofDasymutilla klugii outscored 58 other species of stinging insects tested; the only species this researcher rated as having a more painful sting wereParaponera clavata (bullet ant),Synoeca septentrionalis (warrior wasp), andPepsis andHemipepsis spp. (tarantula hawks).[14] In an experimental setting, only two lizard species (onewhiptail and oneside-blotched lizard) attacked a velvet ant it was exposed to.[12] In both cases the velvet ants were exhibiting rapid lateral and vertical movements to ward off an attack. Once the attack occurred the velvet ants would immediately sting the lizards. This sting resulted in the dropping of the ants in both cases and avoidance for the remainder of the trial.[12] The side-blotched lizard was found dead in its tank 24 hours later.[12] The side-blotched lizard is a natural predator of velvet ants, while the whiptail is not.[12]The aposematic coloration of velvet ants often corresponds to a specificMüllerian mimicry ring consisting of dozens of species. This offers protection because many local predators have learned to avoid prey with this same coloration.[6] To test the aposematic coloration on birds, mealworms were painted to resemble a velvet ant. During these trials, none of the painted mealworms were consumed, while all the control mealworms were consumed immediately.[12] However, the painted mealworms were attacked by the birds, but the birds immediately ceased the attack.[12] These experiments provide evidence that the aposematic coloration of velvet ants causes their predators to hesitate, acting as a visual defense mechanism.
The stridulatory organ that velvet ants possess produces an audible squeaking when the abdomen is contracted.[15] This mechanism is an auditory cue warning predators that are about to attack to stay away. In one experiment, every time ashrew got within 1 meter of a velvet ant, the velvet ant would begin stridulating.[12] Stridulations became more frequent as the predator moved closer to the velvet ant, and the shrew never attempted to attack the velvet ant. However, different scenarios with shrews have shown that the velvet ant would also stridulate after the shrew attacked it. Every time this occurred the shrew dropped the wasp.[12]
The exoskeleton of the velvet ant is remarkably strong. It required 11 times more force to crush than that of the honeybee.[15] As well as being durable, the exoskeleton is also round, making it more difficult for predators to pierce it with attempted stings or bites. During all the trials that led to the fracture of a velvet ant's exoskeleton, a total of 4 times resulted in the death of that velvet ant within 24 hours. Aside from protection from predators, the exoskeleton also helps control moisture.[15]
Due to these strong defense mechanisms, local predators generally avoid the velvet ants, so it has been difficult to determine their predators.[12] One study found tropical and subtropical iguanian lizards (Dactyloidae) to be a local predator of velvet ants in the black-headedTimulla and tropical mimicry rings.[16]
Male mutillids fly in search of females; after mating, the female enters a host insect nest, typically a ground-nesting bee or wasp burrow, and deposits one egg near eachlarva orpupa. Only a few species are known to parasitize other types of hosts;[17] exceptions include the European velvet ant,Mutilla europaea, one of the only species that attacks social bees (e.g.,Bombus), and the genusPappognatha, whose hosts are tree-dwellingorchid bees. The mutillid larvae then develop asidiobiont ectoparasitoids, eventually killing their immobile larval/pupal hosts within a week or two. Velvet ants exhibithaplodiploid sex determination, as do other members of the superfamilyVespoidea.
Recent classifications ofVespoideasensu lato (beginning in 2008) concluded that the familyMutillidae contained one subfamily that was unrelated to the remainder, and this subfamily was removed to form a separate familyMyrmosidae.[18][19]
Media related toMutillidae at Wikimedia CommonsAuthority control databases: National |
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