Mecoptera Temporal range: Early Permian - Recent PreꞒ Ꞓ O S D C P T J K Pg N
Panorpa communis, male
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Insecta
(unranked):	Antliophora
Order:	Mecoptera Packard, 1886 Comstock, 1895
Families
Apteropanorpidae Boreidae (snow scorpionflies) Choristidae †Choristopsychidae[1] †Englathaumatidae[2] Eomeropidae Meropeidae (earwigflies) †Mesopsychoidea (=Aneuretopsychina) †Aneuretopsychidae[3] †Mesopsychidae[4] †Nedubroviidae[3] †Pseudopolycentropodidae[5] Nannochoristidae Panorpoidea †Australochoristidae[6] †Austropanorpidae †Cantabridae †Dinopanorpidae[7] †Eorpidae †Holcorpidae †Orthophlebiidae Panorpidae (common scorpionflies) Panorpodidae (short-faced scorpionflies) †Protorthophlebiidae †Worcestobiidae †Permochoristidae[3] Raptipedia Bittacidae (hangingflies) †Cimbrophlebiidae[8] Siphonaptera? (fleas)

Mecoptera (from the Greek: mecos = "long", ptera = "wings") is an order of insects in the superorder Holometabola with about six hundred species in nine families worldwide. Mecopterans are sometimes called scorpionflies after their largest family, Panorpidae, in which the males have enlarged genitals raised over the body that look similar to the stingers of scorpions, and long beaklike rostra. The Bittacidae, 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, family Boreidae, 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 the Siphonaptera (fleas), and a little more distantly to the Diptera (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 as leaf 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 in pollinating extinct species of gymnosperms 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 a cadaver, making them useful in forensic entomology.^[9]

Diversity

Mecopterans vary in length from 2 to 35 mm (0.1 to 1.4 in). There are about six hundred extant species known, divided into thirty-four genera in nine families. The majority of the species are contained in the families Panorpidae and Bittacidae. 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 the Afrotropic and Palearctic realms, but there is greater diversity at the generic and family level in the Neotropic, Nearctic and Australasian realms. They are absent from Madagascar and many islands and island groups; this may demonstrate that their dispersal ability is low, with Trinidad, Taiwan and Japan, where they are found, having had recent land bridges to the nearest continental land masses.^[10]

Evolution and phylogeny

Taxonomic history

The European scorpionfly was named Panorpa communis by Linnaeus in 1758.^[12] The Mecoptera were named by Alpheus Hyatt and Jennie Maria Arms in 1891.^[13] The name is from the Greek, mecos meaning long, and ptera 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 a clade, containing the Boreidae as sister to the Meropeidae,^[15] but in 2002 Michael F. Whiting declared the Mecoptera so-defined as paraphyletic, with the Boreidae as sister to another order, the Siphonaptera (fleas).^[16]

Fossil history

Among the earliest members of the Mecoptera are the Nannochoristidae of Upper Permian age. Fossil Mecoptera become abundant and diverse during the Cretaceous, for example in China,^[17] where panorpids such as Jurassipanorpa, hangingflies (Bittacidae and Cimbrophlebiidae), Orthophlebiidae, and Cimbrophlebiidae have been found.^[18][19]

Extinct Mecoptera species may have been important pollinators of early gymnosperm seed plants during the late Middle 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 their nectar and pollen. The lack of iron enrichment in their fossilized probosces rules out their use for drinking blood. Eleven species have been identified from three families, Mesopsychidae, Aneuretopsychidae, and Pseudopolycentropodidae within the clade Aneuretopsychina. Their lengths range from 3 mm (0.12 in) in Parapolycentropus burmiticus to 28 mm (1.1 in) in Lichnomesopsyche 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 do bee flies and hoverflies today, but no such associated pollen has been found, even when the insects were finely preserved in Eocene Baltic amber. They likely pollinated plants such as Caytoniaceae, Cheirolepidiaceae, and Gnetales, 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 the Permochoristidae, to the Middle Triassic. During the Late Triassic through the Middle Jurassic, Aneuretopsychina species were gradually replaced by species from the Parachoristidae and Orthophlebiidae. Modern mecopteran families are derived from the Orthophlebiidae.^[22]

• 
  Juracimbrophlebia ginkgofolia (Cimbrophlebiidae) reconstruction, Jurassic; China
• 
  Jurassipanorpa sticta (Panorpidae), Jurassic; China
• 
  Forewing of Dinokanaga andersoni (Dinopanorpidae), Eocene; Washington state

External relationships

Mecoptera have special importance in the evolution of the insects. Two of the most important insect orders, Lepidoptera (butterflies and moths) and Diptera (true flies), along with Trichoptera (caddisflies), probably evolved from ancestors belonging to, or strictly related to, the Mecoptera. Evidence includes anatomical and biochemical similarities as well as transitional fossils, such as Permotanyderus and Choristotanyderus, which lie between the Mecoptera and Diptera. The group was once much more widespread and diverse than it is now, with four suborders during the Mesozoic.^[23]

It is unclear as of 2020 whether the Mecoptera form a single clade, or whether the Siphonaptera (fleas) are inside that clade, so that the traditional "Mecoptera" taxon is paraphyletic. However the earlier suggestion that the Siphonaptera are sister to the Boreidae^[24][16][25] is not supported; instead, there is the possibility that they are sister to another Mecopteran family, the Nannochoristidae. The two possible trees are shown below:^[26]

(a) Mecoptera (clades in boldface) is paraphyletic, containing Siphonaptera:^[26][27]

(b) Mecoptera is monophyletic, sister to Siphonaptera:^[26]

Internal relationships

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. The Eomeropidae is suggested to be the sister group to the rest of the Mecoptera, with the position of the Bittacidae unclear. Of those other families, the Meropeidae is the most basal, and the relationships of the rest are not completely clear.^[28]