I happened upon an insect I’d not seen before while walking at Sidwood in July. I thought it was rather unusual so I took some pictures to help identify it when I returned home. The insect turned out to be a female Scorpionfly, an insect with a long and interesting family history.
Scorpionflies are the only UK representatives of the insect order Mecoptera, derived from the Greek mekos, long, and pteron, wing, and referring to the shape of both the front and hind wings in most species.
In evolutionary terms, the Mecoptera is an old group; fossil specimens have been found from the Permian period, 300-250million years ago. However, the group was far more diverse in prehistory, when there were nine families, than now when only three remain. The Mecoptera are also one of oldest known homometabolous groups, having complete metamorphosis (egg, larva, pupa and adult stages), and as such may be the forerunner of other insects that have complete metamorphosis such as butterflies, moths and caddis flies. To see pictures of fossil Scorpionflies click here
The three present-day families of Scorpionflies are Common (Panorpidae), Snow (Boreidae) and Hanging (Bittacidae). There are some three-hundred species of Mecoptera world-wide of which thirty species can be found in Europe. The Common Scorpionflies, the Panorpidae, are the largest family but only three Panorpa are found in the UK. These are Panorpa germanica, Panorpa communis and Panorpa cognate; they are all so similar that it is impossible to tell them apart without examining their genitalia under a microscope. To read more about Snow and Hanging Scorpionflies click here
It is only the Common Scorpionflies that have the upturned scorpion-like genitalia or 'tail' that gives the order its name. They are brownish yellow and black insects with mottled wings and are found amongst shaded vegetation, such as the one I found at Sidwood, and in hedgerows. To see pictures of other Scorpionflies, including males, click here
The adult Scorpionfly is about 15mm long. Its head is shaped like a beak, as in my picture above; it is this feature that is useful in distinguishing them from other insects and which first attracted my attention. And while the adults look a little scary, they are in fact quite harmless. They feed on dead or dying insects, including any they might spot in a spider's web, and on pollen and flowers. They are also partial to ripe fruit and, when it's available, to human sweat.
Panorpid males attract females by vibrating their wings. When it's time to mate, the males find a good source of food and attract females with pheromones from their enlarged genital segment. When the female approaches, the male exudes a mass of brown saliva, which serves as a nuptial gift. The female chooses a male based on this gift and in response to this, the males have evolved saliva glands so large that they take up most of their body cavity.
After mating the eggs are laid in soil, expanding greatly just before hatching. The larva are caterpillar-like with conical legs. They have compound eyes, which is unlike the larva of most of the other homometabolous insects (for example, caterpillars and beetle larva do not have compound eyes). They can pupate quickly, sometimes in a week and hatch as adults. An illustration of a Common Scorpionfly larva can be found here