The Royal Entomological Society (RES) has a pretty awesome logo. That’s a great looking fly on it, right? Right? While it has the general dipteran ‘look’, with reduced club-like forewings, it’s actually a member of a pretty bizarre order of insects: the Strepsiptera. When the Rev. William Kirby – the first to identify the order – was made honorary RES president in 1833, the Society proudly made a Strepsipteran their mascot. What makes it so special?
The individual on the logo is male. Males looks basic enough, but have some interesting features. Firstly, their compound eyes – which look endearingly like tiny raspberries – are made up of clusters of smaller individual eyes (like trilobites!). Secondly, their mouths are reduced to the point that they’re effectively useless, making feeding impossible; this gives them a Jack Bauer-esque window in which to find a mate. Finally, the wings are big floppy fans that give the order its name, translating as ‘twisted wing’. ‘Twisted’ is, however, a word best reserved for the females…
…Which are just plain odd. Unlike males, they live life as obligate parasites. Hosts vary by species, but include wasps, hemipterans, grasshoppers and cockroaches. They insert themselves between the abdominal segments of their clueless host, peeping out like a nosy neighbour through venetian blinds. Their presence can reduce the host’s secondary sexual characteristics and even lead to castration. For many species, unlimited access to an all-you-can-eat buffet leaves the females rather sedentary, resulting in no need for legs. Or wings. Or eyes. In fact, they don’t look any more developed than the larvae (a state called neoteny). With little else to do for fun, females fill their abdomens to bursting with hundreds to thousands of eggs. When ready, they use their rump as a beacon, releasing pheromones to lure males in. Traumatically, the male delivers sperm by hypodermic insemination. Ouch.
After that romantic episode, the genderless young – triungulins – exit their mother through her brood canal. (The young have six legs, but any attempt to make their mother jealous is stymied by her lack of eyes to see them.) In species that require a wasp or bee to latch onto, the triungulins may ambush a host by waiting in a flower and catching a ride back to the nest. Here they can find an immature and gain entry by dissolving its cuticle with enzyme-rich spit. After growth and finally pupation in the host’s tissues, strepsipteran males emerge and fly away hurriedly, while females stay put, having lost their appendages (not that they have much choice).
The combination of a weird life-cycle and strange physical features have made Strepsiptera and its roughly 600 species difficult to classify. JO Westwood (yet another entomologist with a powerful beard) lamented in early observations that “mere conjecture has endeavoured to supply many points relative to [strepsipteran] economy”, but there was still much to learn. He would certainly would rest easy knowing that much of the “remarkable structure and singular economy” have been untangled and that genetic evidence has finally placed them alongside the Coleoptera (fun fact: Strepsiptera may have the smallest genome of all insects).
So next time you’re sipping from your RES-branded coffee mug and someone asks you about that ‘weird looking fly’ on it, you can help them appreciate this beautiful and somewhat crafty organism.
For more information and pictures: Tree of Life Web Project; American Entomological Society; Academy of Natural Sciences of Drexel University (video); creationsists have (somehow) had a field day with this.