Strepsipterwhat?

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?

RES logo

Royal Entomological Society logo featuring Stylops melittae

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…

Strepsiptera life stages

Strepsiptera life stages: (a) adult male, (b) adult female, (c) female within host’s abdomen, and (d) and (e) larvae (Public Domain, Popular Science Monthly vol. 19)

…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.

Stylopised bee

Three Stylops melittae females poking out from an Andrena vaga abdomen (CC BY-SA 3.0 user Aiwok via Wikimedia Commons)

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).

Strepsiptera mating

A male Stylops melittae alighting on the posterior of an Andrena vaga bee to mate with a female embedded in its abdomen (CC BY-SA 3.0 user Aiwok via Wikimedia Commons)

The combination of a weird life-cycle and strange physical features have made Strepsiptera and its roughly 600 species difficult to classifyJO 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.

Also check out Mike Hrabar’s photostream on Flickr for some great Strepsiptera macrophotography, and this article by Sean McCann on the Entomological Society of Canada blog.

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8 responses to “Strepsipterwhat?

  1. Note that Kirby did not name the order on account of their twisty hind wings, but rather he proposed “Strepsiptera” on account of their haltere-like fore-wing structures, which he likened to “distorted elytra”!

    Kirby thought they were related to beetles! – and after nearly 200 years of bickering placement – relating them to nearly every other insect order, it turns out he was probably right!

    • Thanks Mike, that’s fascinating. The history of entomology is often as interesting as the science itself. Kirby seems to have been rather ahead of his time on the ‘Strepsiptera problem’; did he liken them to Coleoptera because of the supposed ‘elytra’?

      • Yes, Strepsiptera are fascinating on many levels.

        Kirby really did get a lot right about this mysterious order. Prior to his proposing ordinal status, they were placed within the Hymenoptera, in Ichneumonidae, due to their parasitic habit. Kirby placed them nearest to the Coleoptera for several reasons: in addition to what he thought were miss-shapen elytra, he noted similarities with meloid beetles – principally their mobile first instar larval stage, which are to this day referred to as “triungulins” (in reference to the three toed “tri-ungulin” larvae of the Meloe).

  2. This is my second favorite insect order, after Gyrlloblattodea 🙂 Which should not be grouped in an order with mantophasmodea..

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