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Mecoptera

(Scorpionflies and hangingflies)

Class Insecta

Order Mecoptera

Number of families 9

Photo: A scorpionfly (Panorpa communis) in flight. (Photo by Kim Taylor. Bruce Coleman, Inc. Reproduced by permission.)

Evolution and systematics

Classified within the order Mecoptera are perhaps the most primitive insects with complete metamorphosis. The fossil record of Mecoptera is rich, dating back to the lower Permian, when they were one of the most abundant insect groups. The modern orders Trichoptera, Lepidoptera, Siphonaptera, Strepsiptera, and Diptera are believed to have descended from a mecopteran ancestor. The order today is made up of remnants of this former diversity, containing about 600 species in nine families: Apteropanorpidae (1 genus, 1 species); Bittacidae (16 genera, 172 species); Boreidae (3 genera, 27 species); Choristidae (3 genera; 8 species); Eomeropidae (1 genus, 1 species); Meropeidae (2 genera, 2 species); Nannochoristidae (2 genera, 7 species); Panorpidae (3 genera, 360 species); and Panorpodidae (2 genera, 9 species). Living examples of Mecoptera vary widely in form and biology. Because of this extreme diversity, the status of the order as a single evolutionary unit is under debate, and it eventually may be divided into several new orders.

A scorpionfly (Panorpa communis) profile. (Photo by L. West. Bruce

Coleman, Inc. Reproduced by permission.)

Physical characteristics

No single feature unifies the order. Fully winged species share wing structure, having four long, membranous wings,

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Panorpa nuptialis illustrating the various life stages of mecopterans. (Illustration by Wendy Baker)

with both the front and hind pairs similar in shape and venation (number and shape of veins in an insect’s wings). The order name Mecoptera means “long wings.” Mecoptera generally have hyaline (clear) wing membranes with dark veins. When a color pattern exists, it is typically a transparent amber coloration or dark brown banding and striping on the wing membranes. Another common feature is the elongation of the mouthparts and lower portions of the head into a rostrum, a useful character for placing short-winged or wingless species within the order. The mandibles are located at the tip of the rostrum.

Many adult body types exist. Males of Panorpidae and Panorpodidae commonly are called scorpionflies. They have enlarged, bulbous genitalia, carried curled above the body, resembling the tail of a scorpion. The hangingflies, family Bittacidae, look like crane flies (order Diptera), in that they have narrow bodies and long, thin legs. Meropeids and eomeropids are cockroach-like, with flattened bodies and tough, densely veined wings. There are three body types of mecopteran larvae: eruciform (caterpillarlike, with false legs on the abdomen), campodeiform (long

and cylindrical, lacking false legs), and scarabaeiform (grublike).

Distribution

Mecoptera are distributed worldwide, including the northern polar regions. Some families are very restricted in distribution. The highest species diversity occurs in the Indomalayan biogeographical region, which encompasses Southeast Asia and Indonesia.

Habitat

Mecoptera are found chiefly in cool, moist habitats. Forests with plentiful shade support the greatest diversity of species. Most larvae develop beneath soil or litter. Nannochoristid larvae, however, are completely aquatic. Adults of Boreidae, called snow scorpionflies, are found on rocks, snow, and ice in the vicinity of moss clumps, within which their larvae develop.

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Mating in Boreus brumalis is unique, with an unusual posture and the
use of the male’s specially modified spiny wings to hold the female
during the long period of time spent in copulation. (Illustration by Wendy
Baker)	A scorpionfly (Panorpa communis) on a leaf in northern France. (Photo
	by J-C Carton. Bruce Coleman, Inc. Reproduced by permission.)

Behavior

Adult Mecoptera tend to be rather secretive, inactive insects, most frequently found resting on the surface of leaves in dense shade. Flight in most species is feeble and brief. Predaceous species typically feed during the day, while opportunistic species have flexible foraging schedules. Reproductive activity in most species takes place only at night.

Feeding ecology and diet

Mecopterans are carnivorous, herbivorous, or omnivorous. Hangingflies are adapted to a predaceous lifestyle. Their hind legs are raptorial, with a single large tarsal claw, used to capture small insect prey. Prey is pierced with the rostrum, and fluids are withdrawn. Snow scorpionflies apparently are an entirely herbivorous group, feeding on mosses as adults and larvae. Most panorpid scorpionflies are omnivores, feeding opportunistically on dead or dying insects but also on plant secretions such as pollen, fruit juice, and nectar. Mecopteran larvae are mostly omnivorous, an exception being the aquatic larvae of Nannochoristidae, which are predaceous on the larvae of midges (order Diptera).

Reproductive biology

Males court nearby females with displays of wing and body movements, and many offer females a nuptial meal.

Common nuptial meals are prey items and salivary secretions. Competition among males often is fierce, and males that are competitively unsuccessful may attempt to force copulation. Females have been shown to prefer males that offer nuptial meals, and feeding on the meal stimulates egg laying and increases fecundity. Mating may last for several hours. Development progresses through four larval instars, a prepupal stage and a pupal stage. Larval development can be as rapid as one month. Adult life span is of similar duration.

Conservation status

No species of Mecoptera is listed by the IUCN. A decline of mecopteran populations in North America, Mexico, and Java has been noted and is attributable to human activity.

Significance to humans

Mecoptera are not known to affect humans in any way. The common name scorpionfly implies that they are in some way dangerous, but no species stings or bites.

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1. Black-tipped hangingfly (Hylobittacus apicalis); 2. Panorpa nuptialis; 3. Snow scorpionfly (Boreus brumalis). (Illustration by Wendy Baker)

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