Species of the day: Scorpionflies

20 May 2020 | Posted in James Duncan , Insects
Species of the day: Scorpionflies
Scorpionfly male © Nigel Symington

By James Duncan

Learning and Engagement Officer

The Scorpionflies belong to a truly ancient prehistoric order of insects known as Mecoptera, whose ancestry dates back to the Permian epoch, more than 250 million years ago. Fossil evidence suggests that now-extinct species of Mecoptera may have been some of the very first pollinating insects of the earliest seed-producing gymnosperms, plants such as cycads. They diversified extensively during the Creataceous period and these ancestors of today's scorpionflies may well have given rise to both the modern-day 'true flies' (Diptera) and butterflies and moths (Lepidoptera). Around three quarters of the Mecoptera are contained within the family Panorpidae, of which the four species found within the UK belong. One of the most numerous is the Common Scorpionfly (Panorpa communis), though it should be noted that all four are remarkably difficult to tell apart. The scorpionflies are actually widespread across Britain, found in damp, shady habitats, and once spotted it becomes surprising just how numerous these living fossils are. 

The British Scorpionflies are truly bizarre, but rather fabulous looking insects. Their head is highly elongated, extended into a beak-like structure comprising the biting mouthparts. The eyes are large and the body a very distinctive black and yellow. The wings are beautifully patterned and lengthy, giving rise to the very naming of Mecoptera (long-wing), though their flying abilities are actually quite weak. But by far and away the most noteworthy distinguishing feature is the male's enlarged 'scorpion-like' tail that explains their very name. They may sound rather dangerous, but in fact have no string and no ability to inflict any harm upon anything. The red tip to the abdomen really does resemble a scorpion's 'stinger', though is actually the genital capsule. The male first uses this to entice the female in a fancy display of courtship, then to clasp her during the mating process. The striking colouration and 'scorpion' tail certainly seem to exemplify batesian mimicry, where harmless species have evolved to display the warning signals of a harmful species, gifting them increased protection from predators through natural selection. The swollen recurved abdomen is, however, only evident on the males, with the females having a slimmer 'pointed' abdomen.  

The Panorpidae scorpionflies are largely scavengers, feasting mostly on the soft bodies of dead insects and animals, decaying vegetation, rotting fruit and bird droppings. They're not immune from a spot of thievery and often take the opportunity to raid spider webs, feeding on the invertebrates trapped within. The food they collect will ultimately prove critical for reproduction, for the male has a little trick up his six sleeves to attract the female. He'll emit a pheromone to get her attention and should this be successful, surprise her with a nuptial gift. This will take the form of either a dead insect or a salivary mass, which the female will happily consume during copulation. It may not sound too appealing, but the gift directly affects the length of mating and hence the quality and quantity of resulting offspring. The salivary masses can only be provided by the very healthiest of males, so it's a key aspect of sexual selection.

Scorpion Fly © Alan Price, Gatehouse Studio

Scorpionfly © Alan Price, Gatehouse Studio

Scorpion Fly © Neil Fletcher

Scorpionfly male © Neil Fletcher

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