Volume 48, Number 1,
May 2002:
Scorpionflies, Hangingflies, and other Mecoptera

Text-only version

ISSUE HOME PAGE

ABOUT THIS ISSUE
- about KSN
- about the author

IN THIS ISSUE
- The Order Mecoptera
- Fossils
- Modern Species
- Family Panorpidae
- Family Bittacidae
- Family Meropeidae
- Family Panorpodidae
- Family Boreidae
- Key to the Families of North American Mecoptera (Adults)
- References

SLIDESHOW
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Scorpionflies, Hangingflies, and other Mecoptera
by Geroge W. Byers

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

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).

Figure 2. A mating pair of Panorpa flexa in the usual V-position.

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.