Mecoptera (fromAncient Greek μῆκος (mêkos), meaning 'length', and πτερόν (pterón), meaning 'wing') is anorder ofinsects in the superorderHolometabola with about six hundred species in ninefamilies worldwide. Mecopterans are sometimes calledscorpionflies after their largest family,Panorpidae, in which the males have enlarged genitals raised over the body that look similar to the stingers ofscorpions, and long beaklikerostra. TheBittacidae, or hangingflies, are another prominent family and are known for their elaborate mating rituals, in which females choose mates based on the quality of gift prey offered to them by the males. A smaller group is the snow scorpionflies, familyBoreidae, adults of which are sometimes seen walking on snowfields. In contrast, the majority of species in the order inhabit moist environments in tropical locations.
The Mecoptera are closely related to theSiphonaptera (fleas), with some studies suggesting that the fleas are a derived group of parasitic mecopterans, and a little more distantly related to theDiptera (true flies). They are somewhat fly-like in appearance, being small to medium-sized insects with long slender bodies and narrow membranous wings. Most breed in moist environments such asleaf litter or moss, and the eggs may not hatch until the wet season arrives. The larvae are caterpillar-like and mostly feed on vegetable matter, and the non-feeding pupae may pass through a diapause until weather conditions are favorable.
Early Mecoptera may have played an important role inpollinating extinct species ofgymnosperms before the evolution of other insect pollinators such as bees. Adults of modern species are overwhelmingly predators or consumers of dead organisms. In a few areas, some species are the first insects to arrive at acadaver, making them useful inforensic entomology.[9]
Mecopterans vary in length from 2 to 35 mm (0.1 to 1.4 in). There are about six hundredextant species known, divided into thirty-fourgenera in nine families. The majority of the species are contained in the familiesPanorpidae andBittacidae. Besides this there are about four hundred known fossil species in about eighty-seven genera, which are more diverse than the living members of the order.[10] The group is sometimes called the scorpionflies, from the turned-up "tail" of the male's genitalia in the Panorpidae.[11]
Distribution of mecopterans is worldwide; the greatest diversity at the species level is in theAfrotropic andPalearctic realms, but there is greater diversity at the generic and family level in theNeotropic,Nearctic andAustralasian realms. They are absent from Madagascar and many islands and island groups; this may demonstrate that theirdispersal ability is low, with Trinidad, Taiwan and Japan, where they are found, having had recent land bridges to the nearest continental land masses.[10]
The European scorpionfly was namedPanorpa communis byLinnaeus in1758.[12]The Mecoptera were named byAlpheus Hyatt andJennie Maria Arms in 1891.[13] The name is from theGreek,mecos meaning long, andptera meaning wings.[14]The families of Mecoptera are well accepted by taxonomists but their relationships have been debated. In 1987, R. Willman treated the Mecoptera as aclade, containing the Boreidae as sister to the Meropeidae,[15] but in 2002Michael F. Whiting declared the Mecoptera so-defined as paraphyletic, with the Boreidae as sister to another order, theSiphonaptera (fleas).[16]
Among the earliest members of the Mecoptera are theNannochoristidae ofUpper Permian age. Fossil Mecoptera become abundant and diverse during theCretaceous, for example in China,[17] where panorpids such asJurassipanorpa, hangingflies (Bittacidae and Cimbrophlebiidae), Orthophlebiidae, and Cimbrophlebiidae have been found.[18][19]
Extinct Mecoptera species may have been important pollinators of earlygymnosperm seed plants during the lateMiddle Jurassic to mid–Early Cretaceous periods before other pollinating groups such as the bees evolved. These were mainly wind-pollinated plants, but fossil mecopterans had siphon-feeding apparatus that could have fertilized these early gymnosperms by feeding on theirnectar andpollen. The lack of iron enrichment in their fossilizedprobosces rules out their use for drinking blood. Eleven species have been identified from three families,Mesopsychidae,Aneuretopsychidae, andPseudopolycentropodidae within the cladeAneuretopsychina. Their lengths range from 3 mm (0.12 in) inParapolycentropus burmiticus to 28 mm (1.1 in) inLichnomesopsyche gloriae. The proboscis could be as long as 10 mm (0.39 in). It has been suggested that these mecopterans transferred pollen on their mouthparts and head surfaces, as dobee flies andhoverflies today, but no such associated pollen has been found, even when the insects were finely preserved inEoceneBaltic amber. They likely pollinated plants such asCaytoniaceae,Cheirolepidiaceae, andGnetales, which have ovulate organs that are either poorly suited for wind pollination or have structures that could support long-proboscid fluid feeding.[20][21] The Aneuretopsychina were the most diverse group of mecopterans in the Latest Permian, taking the place of thePermochoristidae, to theMiddle Triassic. During theLate Triassic through theMiddle Jurassic, Aneuretopsychina species were gradually replaced by species from theParachoristidae and Orthophlebiidae. Modern mecopteran families are derived from the Orthophlebiidae.[22]
Mecoptera have special importance in the evolution of the insects. Two of the most important insect orders,Lepidoptera (butterflies and moths) andDiptera (true flies), along withTrichoptera (caddisflies), probably evolved from ancestors belonging to, or strictly related to, the Mecoptera. Evidence includes anatomical and biochemical similarities as well astransitional fossils, such asPermotanyderus andChoristotanyderus, which lie between the Mecoptera and Diptera. The group was once much more widespread and diverse than it is now, with four suborders during theMesozoic.[23]
It is unclear as of 2020 whether the Mecoptera form a single clade, or whether theSiphonaptera (fleas) are inside that clade, so that the traditional "Mecoptera" taxon is paraphyletic. However the earlier suggestion that the Siphonaptera are sister to theBoreidae[24][16][25] is not supported; instead, there is the possibility that they are sister to another Mecopteran family, theNannochoristidae. The two possible trees are shown below:[26]
(a) Mecoptera (clades in boldface) is paraphyletic, containing Siphonaptera:[26][27]
All the families were formerly treated as part of a single order, Mecoptera. The relationships between the families are, however, a matter of debate. The cladogram, from Cracraft and Donoghue 2004, places the Nannochoristidae as a separate order, with the Boreidae, as the sister group to the Siphonaptera, also as its own order. TheEomeropidae is suggested to be the sister group to the rest of the Mecoptera, with the position of theBittacidae unclear. Of those other families, theMeropeidae is the most basal, and the relationships of the rest are not completely clear.[28]
^Some studies find Nannomecoptera as sister to the Boreidae+Siphonaptera clade.[16]
^abThe position of theBittacidae is unclear. Two alternative positions, either basal within Mecopterasensu stricto or sister to Panorpodidae, are shown.
MalePanorpa dubia. A, Body in lateral view; B–D. male genital bulb and gonostyli. B, dorsal view; C, ventral view; D, lateral view. ep, epandrium; gcx, gonocoxite; gs, gonostylus; hv, hypovalva; hyp, hypandrium. Scale bars represent 3 mm in A, 1 mm in B–D
Mecoptera are small to medium-sized insects with long beaklikerostra, membranous wings and slender, elongated bodies. They have relatively simple mouthparts, with a longlabium, longmandibles and fleshypalps, which resemble those of the more primitivetrue flies. Like many other insects, they possesscompound eyes on the sides of their heads, and threeocelli on the top. The antennae are filiform (thread-shaped) and contain multiple segments.[23][29]
The fore and hind wings are similar in shape, being long and narrow, with numerous cross-veins, and somewhat resembling those of primitive insects such asmayflies. A few genera, however, have reduced wings, or have lost them altogether. Theabdomen is cylindrical with eleven segments, the first of which is fused to themetathorax. Thecerci consist of one or two segments. The abdomen typically curves upwards in the male, superficially resembling the tail of ascorpion, the tip containing an enlarged structure called the genital bulb.[23][29]
Thecaterpillar-likelarvae have hardsclerotised heads with mandibles (jaws), short true legs on the thorax,prolegs on the first eight abdominal segments, and a suction disc or pair of hooks on the terminal tenth segment. The pupae have free appendages rather than being secured within a cocoon (they are exarate).[29]
Mecopterans mostly inhabit moist environments although a few species are found in semi-desert habitats. Scorpionflies, family Panorpidae, generally live in broad-leaf woodlands with plentiful damp leaf litter. Snow scorpionflies, family Boreidae, appear in winter and are to be seen on snowfields and on moss; the larvae being able to jump likefleas. Hangingflies, family Bittacidae, occur in forests, grassland and caves with high moisture levels. They mostly breed among mosses, in leaf litter and other moist places, but their reproductive habits have been little studied, and at least one species,Nannochorista philpotti, has aquatic larvae.[10]
Adult mecopterans are mostlyscavengers, feeding on decaying vegetation and the soft bodies of dead invertebrates.Panorpa raidspider webs to feed on trapped insects and even the spiders themselves, and hangingflies capture flies and moths with their specially modified legs. Some groups consumepollen,nectar,midge larvae,carrion and moss fragments.[10] Most mecopterans live in moist environments; in hotter climates, the adults may therefore be active and visible only for short periods of the year.[23]
Various courtship behaviours have been observed among mecopterans, with males often emittingpheromones to attract mates. The male may provide an edible gift such as a dead insect or a brown salivary secretion to the female. Some boreids have hook-like wings which the male uses to pick up and place the female on his back while copulating. Male panorpids vibrate their wings or evenstridulate while approaching a female.[10]
Hangingflies (Bittacidae) provide a nuptial meal in the form of a captured insect prey, such as a caterpillar, bug, or fly. The male attracts a female with a pheromone from vesicles on his abdomen; he retracts these once a female is nearby, and presents her with the prey. While she evaluates the gift, he locates her genitalia with his. If she stays to eat the prey, his genitalia attach to hers, and the female lowers herself into an upside-down hanging position, and eats the prey while mating. Larger prey result in longer mating times. InHylobittacus apicalis, prey 3 to 14 millimetres (0.12 to 0.55 in) long give between 1 and 17 minutes of mating. Larger males of that species give prey as big as houseflies, earning up to 29 minutes of mating, maximal sperm transfer, more oviposition, and a refractory period during which the female does not mate with other males: all of these increase the number of offspring the male is likely to have.[30]
The female lays the eggs in close contact with moisture, and the eggs typically absorb water and increase in size after deposition. In species that live in hot conditions, the eggs may not hatch for several months, the larvae only emerging when the dry season has finished. More typically, however, they hatch after a relatively short period of time. The larvae are usually quitecaterpillar-like, with short, clawed, true legs, and a number of abdominalprolegs. They have sclerotised heads with mandibulate mouthparts. Larvae possess compound eyes, which is unique amongholometabolous insects.[31] The tenth abdominal segment bears either a suction disc, or, less commonly, a pair of hooks. They generally eat vegetation or scavenge for dead insects, although some predatory larvae are known. The larva crawls into the soil or decaying wood topupate, and does not spin a cocoon. The pupae areexarate, meaning the limbs are free of the body, and are able to move their mandibles, but are otherwise entirely nonmotile. In drier environments, they may spend several months indiapause, before emerging as adults once the conditions are more suitable.[23]
The raisedscorpion-like tail of the male has earned the scorpionflies a sinister reputation, but they do not sting.
Forensic entomology makes use of scorpionflies' habit of feeding on humancorpses. In areas where the family Panorpidae occurs, such as the eastern United States, these scorpionflies can be the first insects to arrive at a donated human cadaver, and remain on a corpse for one or two days. The presence of scorpionflies thus indicates that a body must be fresh.[32][9]
Scorpionflies are sometimes described as looking "sinister", particularly from the male's raised "tail" resembling ascorpion's sting.[33] A popular but incorrect belief is that they can sting with their tails.[34]
^Novokshonov, V. G.; Ross, A. J.; Cook, E.; Krzemiński, W.; Soszyńska-Maj, A. (2016). "A new family of scorpionflies (Insecta; Mecoptera) from the Lower Cretaceous of England".Cretaceous Research.62:44–51.Bibcode:2016CrRes..62...44N.doi:10.1016/j.cretres.2016.01.013.
^abcBashkuev, A.S. (2011). "Nedubroviidae, a new family of Mecoptera: the first Paleozoic long-proboscid scorpionflies".Zootaxa.2895 (1):47–57.doi:10.11646/zootaxa.2895.1.3.S2CID83075922.
^Krzemiński, W.; Soszyńska-Maj, A.; Bashkuev, A. S.; Kopeć, K (2015). "Revision of the unique Early Cretaceous Mecoptera from Koonwarra (Australia) with description of a new genus and family".Cretaceous Research.52:501–506.Bibcode:2015CrRes..52..501K.doi:10.1016/j.cretres.2014.04.004.
^Bashkuev, A. S. (2011). "The earliest Mesopsychidae and revision of the family Mesopanorpodidae (Mecoptera)". In Shcherbakov, D.; Engel, M.; Sharkey, M. (eds.).Advances in the Systematics of Fossil and Modern Insects: Honouring Alexandr Rasnitsyn. ZooKeys 130. Vol. 130. PenSoft. pp. 263–279.doi:10.3897/zookeys.130.1611.ISBN978-954-642-609-3.PMC3260765.PMID22259282.
^abcdeHoell, H.V.; Doyen, J.T.; Purcell, A.H. (1998).Introduction to Insect Biology and Diversity, 2nd ed. Oxford University Press. pp. 488–491.ISBN978-0-19-510033-4.
^Wiegmann, Brian; Yeates, David K. (2012).The Evolutionary Biology of Flies. Columbia University Press. p. 5.ISBN978-0-231-50170-5.Recently, a close affinity between Siphonaptera and Mecoptera has been convincingly demonstrated via morphology (Bilinski et al. 1998) and molecular data (Whiting 2002), rendering Mecoptera paraphyletic, but making the clade including Mecoptera and Siphonaptera monophyletic
^abcMeusemann, Karen; Trautwein, Michelle; Friedrich, Frank; Beutel, Rolf G.; Wiegmann, Brian M.; et al. (2020). "Are Fleas Highly Modified Mecoptera? Phylogenomic Resolution of Antliophora (Insecta: Holometabola)".bioRxiv10.1101/2020.11.19.390666.
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