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Bug of the Month: Common scorpionfly

common scorpionfly - sideCommon name: Common scorpionfly

Latin name: Panorpa rufescens

Taxonomy:
Kingdom Animalia
   Phylum Arthropoda
      Class Insecta
         Order Mecoptera
            Family Panorpidae

Scorpionflies in general

snout of scorpionflyThe order Mecoptera includes both hangingflies and scorpionflies. There are about 600 described species world-wide, and just 100 species known in North America. Although this order of insects is not very diverse today, fossil evidence suggests that it is one of the oldest groups of insects with complete metamorphosis, and was far more diverse over 200 million years ago. The Mecoptera are thought to be most closely related to true flies (Diptera) and fleas (Siphonaptera).

Almost all species of scorpionflies have distinctively long “beaks” which makes them easy to recognize as a group. A resemblance to scorpions is evident only among species in the family Panorpidae, the family most commonly seen in eastern North America. Males of these species have what looks like a scorpion stinger at the end of their abdomen that arches up and over their backs. The “stinger” is actually the male genitalia, and has no stinging or defensive function.

Within the “common scorpionflies” (family Panorpidae), there are about 50 species in eastern North America (all in the genus Panorpa), and most do not have common names, including Panorpa rufescens. The more general information below is probably true for most Panorpa species. At present we do not know how many species of Panorpa, in addition to P. rufescens, occur on the Boston Harbor Islands.

scorpionfly genital

overhead view of male scorpionflyHow to identify common scorpionflies

All species in the genus Panorpa have a long snout; yellow, orange, or reddish bodies; and clear or yellowish wings patterned with dark bands and spots. Males have a distinctive scorpion-like genital bulb. While wing pattern can be used to identify a few species, the most reliable way to differentiate between species is by looking at the male genitalia under high magnification. Therefore, field identification of the species P. rufescens is not usually possible!  However, it is relatively simple to recognize the Panorpa genus.

Where to find common scorpionflies on the Boston Harbor Islands

Look for scorpionflies in shady, wooded habitats with a lush herbaceous understory. Scorpionflies are typically scavenging for food on the leaves just a few feet off the ground (so look down!). If disturbed, the scorpionfly will often hop to another leaf, or drop down to the ground.

How common scorpionflies make a living

The main diet of scorpionflies is dead and dying soft-bodied insects. Scorpionflies are known to be “kleptoparasites” meaning they will steal prey that has been captured by predators such as spiders. In fact, scorpionflies will scavenge on prey trapped in spider webs, and then regurgitate a fluid that deters the spider! However, scorpionflies do often become prey for spiders as well as for hunting insects like damselflies, robber flies, and predaceous true bugs.

In courtship, the male emits a pheromone and offers a female an item of food (either a dead insect or a pellet of congealed saliva!), both of which serve to lure in the female so that the male can clasp her with the end of his abdomen and begin mating, while she feeds.

The female lays her eggs in existing cavities in the soil, and for many Panorpa species these hatch within five to ten days. Immature scorpionflies look like caterpillars, but they are unlike the larvae of any other insects in having true compound eyes of 30 or more divisions. The larvae will go through several molts, growing larger, before burrowing into the soil to go through a period of diapause (inactivity) and then to pupate. The inactive stage may last weeks to months, while the pupa develops within 10 to 20 days, leading to the emergence of an adult scorpionfly.

Where in the world common scorpionflies occur

P. rufescens is recorded from many states in the northeastern U.S., as far south as the District of Columbia, and as far west as Michigan. The genus Panorpa is found only in the eastern part of North America, and about 90 additional species are known from Europe and Asia.

To learn more about common scorpionflies (and Mecoptera in general)

On the web:

In print:

    Byers, G.W. and R. Thornhill. 1983. Biology of the Mecoptera. Annual Review of Entomology. 28: 203-228.

    Jennings, D.T, and N.J. Sferra. (2002). An arthropod predator-prey kleptoparasite association. Northeastern Naturalist: 9: 325-330.

    Thornhill, A.R. and J.B. Johnson. 1974. The Mecoptera of Michigan. Great Lakes Entomologist, 7:33-53.

    Webb, D.W., N.D. Penny, and J.C. Marlin. 1975. The Mecoptera, or Scorpionflies, of Illinois. Illinois Natural History Survey Bulletin, 31:251-316.