Scorpionflies, Hangingflies, and other Mecoptera
by George W. Byers
ABOUT THIS ISSUE
Kansas School Naturalist
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Cover: A pair of Panorpa mirabilis mating on forest undergrowth, a common habitat for panorpid scorpionflies.
Photo Credit: All photos in this issue were taken by Mr. Wes Bicha who began photographing scorpionflies 30 years ago after reading an article by Dr. Byers.
ABOUT THE AUTHOR
Dr. George Byers is Entomology Professor Emeritus at the Snow Entomological Division of the Museums of Natural History at the University of Kansas. He is the world authority on scorpionflies as well as a systematist of crane flies. The K.U. museum has by far the largest collection of scorpionflies, including type specimens, in the world.
SCORPIONFLIES, HANGINGFLIES, AND OTHER MECOPTERA
by George W. Byers
Although there are parts of North America where these insects are fairly common and may attract the attention of general collectors, they appear never to be common in Kansas and are not often captured by students collecting for biology classes, 4-H clubs, Boy Scouts, and the like. This is because there are fewer than a dozen species known to occur in Kansas, and most of these are limited to the eastern part of the state, where their habitats are fragmented and the insects are rarely encountered. One may reasonably ask, therefore, why an issue of the Kansas School Naturalist is devoted to such an obscure group of insects.
THE ORDER MECOPTERA
How can members of this group of insects be recognized? How are Mecoptera different from somewhat similar insects in the orders Diptera (flies) or Neuroptera (lacewings)? Briefly, most Mecoptera have four membranous wings with several cross-veins. The wings often have spots or transverse bands of darker color. Hind wings are slightly shorter than the fore wings and have similar markings. A few species, but none in or near Kansas, are wingless or have very small wings (see Kansas School Naturalist, Vol. 38, No 2, p. 15; May 1992). Mecoptera have chewing mouthparts at the end of a beak-like downward prolongation of the head.
Scorpionflies (Family Panorpidae) and hangingflies (Family Bittacidae), together with some smaller families, make up the Order Mecoptera. This is now one of the minor orders of insects, with only about 550 species currently known worldwide. Why then are the Mecoptera of particular interest to entomologists and others concerned with animal evolution? On the basis of various characteristics, but mainly venation of the wings, Mecoptera are judged to be an ancient group of insects, ancestral to such modern and very much larger orders as Diptera (flies) and Lepidoptera (moths and butterflies). Much of the fossil record of insects, from the Carboniferous period onward, is based on wing venation because wings are of a chemical composition that resists decomposition. In sedimentary rocks of the lower Permian geological period (about 270 million years ago), in which insects with complete metamorphosis (having four developmental stages: egg, larva, pupa, and adult) first appear, the Mecoptera are well represented (see Kansas School Naturalist, Vol. 46, No 1, pp. 12–13; Feb. 2000). Fossil Mecoptera of various geological ages have been assigned to about 350 species in 87 genera and 34 families, diversity much greater than among living forms. Only 34 genera in nine families are recognized among mecopterans alive today. Living panorpids and bittacids may be thought of as survivors of an estimated 270 million years of mecopteran evolution.
Figure 1. The tail of a male Panorpa helena Byers shows why some Mecoptera are called “scorpionflies.” This species was named for Dr. Byers’ mother, Helen Byers.
Family Panorpidae first appears in the fossil record as two species of Panorpa in the Baltic amber of Oligocene age (about 35 million years ago). A beautifully preserved panorpid is the more recent Holcorpa maculosa Scudder, of Miocene age, from Florissant, Colorado (photo in Carpenter 1931b, p. 406).
The oldest known species of the Family Bittacidae is Probittacus avitus Martynov, from Jurassic rocks of Turkestan, perhaps 160 million years old. In North America, an excellent example of fossil Bittacidae is Paleobittacus eocenicus Carpenter, of the Green River formation of Eocene age (see Carpenter 1928, plate 12).
Figure 2. A mating pair of Panorpa flexa in the usual V-position.
The nine families of extant Mecoptera have a variety of geographical distributions. Two of these families, Eomeropidae, with the single genus Notiothauma in southern South America, and Apteropanorpidae, including only Apteropanorpa in Tasmania, Australiea, have limited ranges. They will not be considered further here. Two other families, the Choristidae, with three genera in Australia, and the Nannochoristidae (two genera), with the zoogeographically fascinating occurrence in Australia, New Zealand, and southern South America, will also not be dealt with further in this pamphlet.
Family Panorpodidae occurs in the Appalachian region and in the Pacific Northwest in North America, as well as in eastern Asia. Boreidae are found in eastern North America and in the Rocky Mountains and Pacific States. Since species of neither of these families have been found anywhere near Kansas, they will be discussed only briefly, later.
Three families remain. The Panorpidae (a single genus in North America, Europe and Asia, and two more genera in Asia), the Bittacidae (with 17 genera, widespread in North America, South America, Europe, Africa, Asia, and Australia), and the peculiar little family Meropeidae (one genus with one species in eastern North America and another genus with only a single species in southwestern Australia). Representatives of all these three families have been found in Kansas, to some extent. Since these families differ in various aspects of their biology, they will be discussed separately.
These are the scorpionflies, so called because in males the ninth abdominal segment (genital segment) is enlarged, and segments 7 and 8 are relatively slender (Figure 1). The ninth segment is usually carried upward and forward, above the back, a position somewhat resembling that of a scorpion’s stint. (But the insect is quite harmless.) The abdomen of the female tapers backward to a slender tip bearing two small, finger-like cerci. Scorpionflies are likely to be encountered in wooded habitats in which there are broad-leaved, herbaceous plants growing in rich, shaded soil. Rarely they occur in unshaded environments. The insects are usually found standing on the upper surface of leaves about 1–3 feet off the ground. When alarmed, they usually fly to another leaf a few feet away, but if threatened they often drop to the ground.
The diet of adult scorpionflies includes dead or dying insects or, less often, other dead organisms, such as mice or frogs. They have been seen feeding on insects trapped in spider’s webs, but occasionally they become ensnared themselves. There are published accounts of scorpionflies feeding on pollen and associated parts of flowers. Larval panorpids are also scavengers, having much the same diet as the adults.
Mating behavior in Panorpidae usually involves the offering, by the male, of some kind of food. This may be a dead insect or, often, a short column of a brown salivary secretion that becomes gelatinous as it dries in the air. When a suitable dietary item is found, or provided, the male emits a pheromone (an air-borne chemical signal) from vesicles within the enlarged ninth abdominal segment. A female is attracted to the pheromone or the food, whereupon the male grasps the end of her abdomen with the claw-like appendages on his genital segment (dististyles). He also clamps the costal (front) edge of one of the female’s fore-wings in a structure on the mid-dorsal part of his abdominal segments 3 and 4 (the notal organ). Mating then takes place as the female feeds. During mating, the pair forms approximating a V-shape (Figure 2).
Lacking a well-developed ovipositor, the female probes in loose soil to find small openings in which to deposit here eggs. In Panorpa, the eggs are ovoid but about equally rounded at the ends. The chorion (egg shell) is smooth in some species; in others, it is covered by a mesh of polygonal cells. The egg stage has been recorded as 5–10 days in some American panorpids. Near the time of hatching, eggs increase noticeably in size (as much as 38%), and the dark mandibles and eyes of the developing larva become visible through the chorion. The first-stage larva has a sharp “egg-tooth” (or egg-burster) on the frons (front of the head, between the eyes) by means of which it can rip the chorion, at hatching.
Larvae of Panorpa (and some other Mecoptera) are remarkable in having compound eyes, that is, eyes of many (30 or more) ommatidia, or subdivisions. This condition is unknown among larvae of other insects having complete metamorphosis.
Panorpid larvae are caterpillar-like in general appearance, the head sclerotized (hardened) but most of the body nearly membranous, with setae (hairs) projecting from the dorsal and lateral surfaces of the segments. The three pairs of thoracic legs are nearly conical, as are the smaller prolegs (not true segmented legs) on the first eight abdominal segments.
Duration of larval life is influenced by several factors, among which are temperature, availability of food, length of diapause before transformation to the pupal stage, and of course the species involved. In the laboratory, larvae of one species of Panorpa passed through three developmental states and began a fourth in about a month. In the fourth and final larval phase, growth and feeding continued for several days, after which the larva prepared a cavity in the soil and in it became quiescent and began pre-pupal diapause (inactivity). This diapause lasts only about five weeks in species of Panorpa that reach adulthood in late summer. In species that overwinter, it lasts 6.5 to 7 months.
Following the final larval molt, the pupa may complete its development (i.e., of the adult within) in 10–21 days. The pupa has much the shape of the adult, except that the legs are folded loosely against its ventral surface, and the wings are tightly compressed within their sac-like sheaths. The prolongation of the head is much less in the pupa than in the adult.
Figure 3. A mating pair of Hylobitticus apicalis hang from overhead support while the female feeds.
Hangingflies have a single, large claw at the end of each tarsus; they are unable to stand on a surface but suspend themselves from edges of leaves or from twigs. Their wings are elongate, slender toward the base, and usually held down alongside the abdomen except in flight. Some bittacids may be found in shaded habitats together with scorpionflies, but others occur at edges of woodlands or in unshaded places, such as in tall grasses.
Adult hangingflies are predators, feeding on other insects, which are usually captured by the raptorial hind tarsi and held up to the mouth. Bittacids may fly upward along a plant stem and pluck off unwary prey. Only soft parts are eaten. Larvae of Bittacidae feed on dead insects.
Mating behavior of hangingflies has similarities to that of scorpionflies. A male first captures a suitable food item (and may feed on it briefly himself), then emits a pheromone from vesicles everted between sclerites 6–7 and 7–8 on the back of the abdomen. When a female is attracted to the pheromone and appears to judge the food offering adequate, mating ensues, with both partners hanging from overhead support and the female feeding (Figure 3).
Female bittacids show no particular concern for the welfare of their young. When ready to oviposit, the female suspends herself above probably suitable habitat and drops here eggs, one by one. The eggs fall among dead leaves and other debris on the ground, there to lie until hatching. Eggs of most bittacids are unusual in being nearly cuboidal, with each surface slightly impressed. Near the time of hatching, the egg enlarges somewhat and becomes roughly spherical. Duration of the egg stage varies greatly according to the species (Setty 1940).
Larvae of Bittacus (and other bittacids) have compound eyes but with only seven ommatidia each; they also have one ocellus at the top of the frons (front of the head). They are eruciform (that is, they resemble caterpillars), with the head sclerotized but most of the body except the dorsum of the first thoracic segment, virtually membranous, with a pair of branched, fleshy projections on the back of the hind two thoracic segments and abdominal segments 1–9, with smaller appendages at the sides. Bittacid larvae do not burrow into the soil but remain at the surface, concealed by vegetational debris; they may excrete fluid containing soil and deposit this on their dorsal projections, where it adheres and hardens. Setty (1940) has described and illustrated the morphology of adults, larvae of various instars, pupae and many other details, based on his many careful studies of Bittacidae.
Figure 4. A species of Apterobittacus from California lacks wings.
Represented in North America by a single species, Merope tuber, this family also includes a species in Australia. The American species was known in the Atlantic states for many years but considered quite rare. Adults are nocturnal but phototactic (attracted to lights), and increased use of light traps—and also of flight-intercept and chemical traps—in recent years has led to finding that Merope is actually widespread, currently known from southeastern Canada to Georgia and westward to eastern Kansas and Minnesota. The habitat is much the same as for Panorpidae.
These are yellowish brown insects, about 8–15 mm long; body length and wing length vary greatly in both males and females. Their grayish wings are divided into many cells by numerous cross-veins. Males are characterized by elongate, slender clasping structures at the end of the abdomen; the shorter abdomen of females tapers to a narrow tip. Larvae of Merope have not yet been discovered. Virtually nothing is known about the behavior of meropeids other than their response to light.
North American panorpodids, all in genus Brachypanorpa, have been found in the Appalachian Mountains and the mountainous Pacific Northwest. They differ from Panorpidae in having a conspicuously short rostrum and unmarked, yellowish brown wings (Figure 5), as well as some less obvious structural characteristics. Females of some species are brachypterous (very short-winged) and flightless; those of other species have somewhat reduced wings and are poor fliers. The diet of adults is not clear, but they have been observed scraping the surfaces of herbaceous leaves with their mouthparts.
Larval Panorpodidae are eyeless. Lacking prolegs on the ventral side of the abdomen and thick setae (as in Panorpidae) or fleshy projections (as Bittacidae) on the back, the larvae are described as scarabaeiform (resembling larvae of scarab beetles).
Figure 5. Brachypanorpa carolinensis is an example of a panorpodid.
These small (length 2–5 mm), darkly colored mecopterans are most often and most easily seen on snow. They are boreal, the adult stage being attained in winter or at high elevations in mountains, or at high latitudes, such as in Alaska. As far as is known, the diet of both larvae and adults consists of leafy parts of bryophytes (mosses and liverworts). The mating behavior of Boreus, our only common genus, differs from that of other Mecoptera. The male grasps the female with his slender, hardened wings and moves her to a position above his back, with the lower part of her elongate ovipositor inserted into his ninth (genital) segment (Figure 7). Larval boreids, like those of Brachypanorpa, lack abdominal prolegs and conspicuous dorsal setae; they do, however, have lateral eyes, usually each with three ommatidia (visual units). Some systematists have placed Boreidae in a separate order from Mecoptera.
Figure 6. An adult male Boreus on snow.
Key to the Families of North American Mecoptera (Adults)
|1.||Tarsi each with a single, large terminal claw; wings long, narrow, tapering toward base||
|Tarsi each with two small claws; wings not slender near base||
|2.||Wings sclerotized (hardened), without venation; those of male slender, tapering toward apex, with apical spine; those of female small, oval or rounded pads||
Wings membranous, with distinct veins
|3.||Wings broadly rounded at apex, with 12 or more cross-veins along costal (anterior) edge and more than 50 elsewhere on fore wing||
|Wings narrowly rounded at apex, with fewer than three cross-veins along costal edge and fewer than 25 elsewhere on fore wing||
|4.||Ventral prolongation of head (rostrum) long and tapering toward tip||
|Ventral prolongation of head short; conspicuous “tooth” on lower face at each side of rostrum||
Figure 7. A mating pair of Boreus snow scorpionflies.
Beckemeyer, R. J. 2000. The Permian Insect Fossils of Elmo, Kansas. Kansas School Naturalist 46: 1–16.
Byers, G. W. 1963. The Life History of Panorpa nuptialis (Mecoptera: Panorpidae). Annals of the Entomological Society of America 56: 142–149.
Byers, G. W. 1973. Zoogeography of the Meropeidae (Mecoptera). Journal of the Kansas Entomological Society 46: 511–516.
Byers, G. W. 1997. Biology of Brachypanorpa (Mecoptera: Panorpidae). Journal of the Kansas Entomological Society 70: 313–322.
Byers, G. W. and R. Thornhill. 1983. Annual Review of Entomology 28: 203–228.
Carpenter, F. M. 1928. A Scorpion-fly from the Green River Eocene. Annals of the Carnegie Museum18: 241-246, plate 12.
Carpenter, F. M. 1931a. Revision of the Nearctic Mecoptera. Bulletin of the Museum of Comparative Zoology(Harvard University) 72: 205–277, plates 1–8.
Carpenter, F. M. 1931b. The Affinities of Holcorpa maculosa Scudder and Other Tertiary Mecoptera, with Descriptions of New Genera. Journal of the New York Entomological Society 39: 405–414, plate 33.
Schrock, J. R. 1992. Snow Flies. Kansas School Naturalist 38: page 15.
Setty, L. R. 1940. Biology and Morphology of Some North American Bittacidae (Order Mecoptera). The American Midland Naturalist 23: 257–353.
Thornhill, R. 1976. Sexual Selection and Nuptial Feeding Behavior in Bittacus apicalis (Insecta: Mecoptera). The American Naturalist 110: 529–548.
(Back cover) Taeniochorista pallida, a scorpionfly from Queensland, Australia.
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