SCORPIONFLIES AND THEIR RELATIVES (MECOPTERA) OF BRITISH COLUMBIA

Boreus californicus female, photo by Baldo Villegas

by

R. A. Cannings and G. G. E. Scudder 

Copyright © 2005 - All rights reserved

Introduction

The Mecoptera is a minor insect order of about 500 described species arranged in nine families. There are about 83 species known in North America. Although small, the order is diverse and is of great evolutionary interest, because it is closely related to the stem groups of the Diptera, Siphonaptera, Trichoptera and Lepidoptera (“Panorpoid Complex”). The Mecoptera possibly contains the sister group of the Diptera. The order originated in the Permian.

There are five families in North America.

• The Boreidae (snow scorpionflies) is a family of small, flightless insects that are active as adults mainly in the winter. This is BC’s only mecopteran family;
• The Panorpidae (common scorpionflies) contains most of the species in the order -- about 300 world wide, living mainly on the northern continents. The genitalia of the male give the family its name – these structures are large, bulbous and often flexed forward over the abdomen, looking something like a scorpion’s sting. In North America, the 54 described species are placed in the mainly eastern genus Panorpa. The five species of Panorpodidae (short-faced scorpionflies) live in the southern Appalachian Mountains;
• Members of the Bittacidae (hangingflies) look a little like a large, four-winged crane fly (although one western US species is wingless); they hang from vegetation by their front or middle legs and capture insect prey with the hind pair. There are about 145 known species; the family is especially diverse in South America and Australia and contains the only African mecopterans;
• The Meropeidae are called earwigflies because the male has long, terminal abdominal appendages that resemble the pincer-like cerci of earwigs. There are only two species, one in eastern North America and the other from western Australia.

Most scorpionflies live in moist, shady habitats, especially among vegetation in broad-leaved forests, where the adults are herbivors, scavengers or predators, depending on the group. Many feed on fluids such as nectar and honeydew. They usually lay their eggs in the soil and the larvae, which are mostly caterpillar-like, feed on a wide range of dead and decomposing animal matter. The most obvious exceptions are the aquatic Nannochoristidae of South America, Australia and New Zealand, whose larvae prey on chironomid and other fly larvae; the flightless Boreidae of the Northern Hemisphere, which feed on mosses in both the larval and adult stages and whose adults are often active on snow; and the Tasmanian Apteropanorpidae, which resemble the Boreidae in form and habits. Adults and larvae of the Panorpidae are typical practitioners of the scavenging life, feeding on dead insects – often stealing prey from spider webs. Males offer an insect carcass to females as an inducement to mate; if a carcass is unavailable, a pile of saliva is used instead. Larval Bittacidae also often eat dead insects, but the adults are predators, snaring small flying prey with their hind legs while hanging from twigs or leaves.

Mecopterans are small to large insects; boreids can be as small as 2 mm long and some bittacids are over 25 mm long with wingspans of over 50 mm. The body is usually slender and soft. Most species have a distinctive, down-turned, beak-like prolongation of the front of the head with biting mouthparts at the tip. In some Nannochoristidae the mouthparts are specialized for sucking. The compound eyes are large and all families except the Meropeidae and Apteropanorpidae have ocelli. The antennae are long and threadlike, usually about half the body length, with about 16 to 60 segments. Most mecopterans are winged, but some have the wings reduced or absent. Fully winged forms have two pairs of long, rather narrow, membranous wings, with the fore and hind wings similar in size, shape and venation. The venation is generalized, characterized by numerous crossveins. Dark spots and bands occur on the wings of many panorpids and some bittacids. The legs are long and slender; the tarsi are 5-segmented, the fifth bearing two claws in all but the Bittacidae. In this family, a single, enlarged tarsal claw, along with tarsal segment 5, folds back on segment 4, forming a raptorial tarsus.

Reference

Penny, N.D. 1977. A systematic study of the genus Boreus (Mecoptera: Boreidae). University of Kansas Science Bulletin 51(5): 141-217.