The name Scorpion Fly applies to the fact that some male Mecopterans tend to carry their genitallia in an upturned position, giving it some resemblance to the tail of a Scorpion, i.e. Panorpidae and Boridae. Besides this Scorpion flies are recognised by their beak like head and clear spotted wings. They are also known as hanging flies because some species such as Bitticus italicus hang from the vegetation with their front legs and catch small the insects they prey on in their hind legs.
The Scorpion Flies (Mecoptera)
There are more than 500 named species of of Mecoptera and they are among the oldest of they holometabolous (having a complete metamorphosis i.e. egg, larval instars which does not resemble the adult, pupa and then the adult or imago) insectsdating from the Lower Permian 250 million years ago.
They are described as; small to medium sized slender insects with long filiform antennae. The head is extended into a deflexed rostrum or beak with biting mouthparts at its end and is not broader than the front of the thorax, the eyes are prominent and semi-globose. The legs are long and slender, as are the 2 pairs of nearly equal wings which are also membraneous and clear with various dark patterns. The larva are generally eruciform (like a catapillar), but may be modified scarabeiform (grub like, with a well developed head, a thick cylindrical body and 3 pairs of thoracic legs, but no prolegs) i.e. Boridae and Panorpidae, or campodeiform (elongate and flattened with well developed legs and antennae) as in the Nanochoristidae. They have biting mouth parts and 3 pairs of thoracic legs. The pupa is exarate (having its appendages i.e. legs antennae etc. free outside of the main body of the pupa) and dectitious.
The eggs of Scorpion flies are unusual in that they expand as the embryo develops within, by as much as 100% in some genera. Egg development can be as short as 5-10 days (below 1 000 metres) in some species of Panorpa and Neopanorpa, or many months long in those species which overwinter as an egg i.e. Bittacus stigmaterous.
The larvae of some Scorpion Flies (i.e. Panorpa, Neopanorpa and Chorista)are unusual amonst the holometabolous insects in that they have truly compound eyes with 30 or more omatidia (one lens and its accompanying bits and pieces in a compound eye) rather than the simple ocelli more normal of the higher insects.
Larva are believed to be saprophagous (feeding on dead and decaying organic matter) on dead insects in general, often from a burrow excavated underneath the dead insect. The Nannochoristidae have aquatic larvae which prey on Chironimid larva. Some species are known to be herbivorous or partly so, the larva of various Boreids have been observed feeding on mosses
The prepupal stage may last only a month in those species which are semivoltine (having 2 generations a year) to many months in those which are univoltine (having one generation a year) and which overwinter as the prepupa. Pupation occurs in the cell in the soil excavated by the larva and after about 10-50 days the adult or imago emerges.
The Adult or Imago
Mating in the Mecoptera is complex, varied and fascinating, it is hard to generalize about the whole Order; except to say that it all starts when a male emits pheromone which attracts females and in some cases other males as well, but here are a couple of scenarios to wet your appetite.
In the genus Panorpa choose one of three different mating strategies. 1) A male offers a female who has been attracted a food gift which she feeds on during copulation. 2) This is really a variant of 1 except that the male either finds a dead arthropod, feeds on it a bit then stands beside it while emitting his pheromone attractant, or he secretes a salivary mass onto a leaf or other suitable substrate then stands beside this and emits his pheromone. In both these cases as above copulation takes place while the female is feeding, either on the arthropod or on the salivary secretion. 3) This option is called forced copulation, a male using this stategy does not emit any pheromones or supply any food he simply rushes at her and attempts to mate often succeeding. After mating females become unreceptive to the male pheromone and begin laying eggs
In the genus Hylobittacus males first acquire a dead arthropod after feeding on it briefly he either discards it (in which case he seeks out another one) or holding the prey with his hind legs he flies from place to place, each time he stops he emits some of his pheromone and waits a short while for a female to respond. An attracted female starts to feed on the arthropod, if it is suitable she stays and copulation occurs. If for some reason she finds it unsuitable she flies of and looks for another male either immediately or after copulation has started but before sperm transfer has occurred. Males actively steal prey from one another and one of the variety of tricks males use to successfully pillage from each other is imitating a female.
Boreids lay their eggs singly among moss while female bittacids drop theirs to the ground while hanging by their for limbs from the vegetation.
Byers, G. W. and Thoynhill, R. (1983). Biology of the Mecoptera. Annual Review of Entomology 28, pp 203-228.
Carpenter, F. M. (1931). The Biology of the Mecoptera. Psyche 38 pp 41-55.
Other Mecoptera Web Sites
A checklist of Genera of Mecoptera
Mecoptera catalogue at UMMZ
Species List University of Michigan Museum of Zoology