by Matthew Cobb
Strepsiptera are some of the world’s weirdest insects. They look weird, they act weird and, like many parasites, they have a very weird life-cycle. Over 600 species have been described and they are all parasitoids, attacking insects from seven different orders – silverfish, flies, crickets, wasps… A parasitoid is an organism that lays its eggs inside another organism, often, but not always, with catastrophic effects for the host. Strepsiptera seem to be an exception, for the host is generally able to survive rearing alien offspring within their bodies – in this sense strepsipterans are closer to parasites than parasitoids.
There is a huge dimorphism between the two sexes. The tiny males (2 mm long) are free-flying with odd, forwardly-curved, twisted wings (hence the name Strepsi-ptera). Once they hatch from their pupa (Strepsiptera are holometabolous, that is, they have a full metamorphosis), males live for only a few hours, and have only one job in life: to find a mate.
In flies, as we have discussed a number of times, the rear pair of wings are reduced to form halteres or balancers, which aid in flight. In Strepsiptera, the same process has taken place but it has involved the front pair of wings. How does this affect how the male flies? Do they have exactly the same function as in flies?
They also have weird branched antennae, odd globular eyes and vicious scissor-like mandibles. Check it out – have you ever seen anything like it? What do the males use those mandibles for? Can you guess (answer below)?
Although these eyes look weird, they are similar to some nymphs in hemimetabolous insects (that is, those insects that do not have full metamorphosis but instead have a series of moults). Intriguingly, male larval Strepsiptera also develop wing buds, like some hemimetabolous nymphs.
They’ve looked like this for a very long time, as shown by this specimen, trapped in a piece of 50-53 million year old Eocence amber from China:
Here’s a male emerging from his hapless host:
A close-up video shows exactly why the male has those snippy-snippy mandibles. Pay attention to the left-hand side of the image – you can just make out the mandibles in action from the first seconds. This is stupendous filming from Mike Hrabar:
The females are even stranger, and are rarely seen, for the simple reason that they spend virtually all their life inside their host. To mate, the female moves down to the abdomen of the host, and pushes a specialised organ out from between the abdominal plates. The poor old host can be carrying a number of these:
The female then exudes a pheromone, which attracts the male. Mating, when it happens is joyless and brief, as show by this rather creepy video by Mike Hrabar:
When the host lays eggs, or returns to the nest in the case of a social insect host, the female strepsipteran lays live offspring that wriggle off and, in ways that remain obscure, locate a new larval host and find their way in; they then grow within the larva (or nymph if the host is a grasshopper), going through three larval stages before finally pupating. If the host is a holometabolous insect, the strepsipteran sits inside the pupa, finding its way to the right place when the adult insect emerges. Gruesome.
(Because this is biology there are of course exceptions; in one strepsipteran family the female is free-living and pupation occurs outside the host.)
Last year there was an excellent paper in The Canadian Entomologist by Mike Hrabar and colleagues, which described in some detail the life-cycle of one strepsipteran species, Xenos peckii which parasitizes wasps (many of the photos and videos here are taken from this paper, and from Sean McCann’s excellent accompanying blog post). Here’s a description of the life cycle of X. peckii:
Until recently the evolutionary position of Strepsiptera was a matter of debate, although most people agreed they were related to the Coleoptera, or beetles. Over the last couple of years, however, all that has been resolved, with two separate genomic studies comparing the DNA of Strepsiptera with that of other insects. Both studies agree that Strepsiptera are most closely related to Coleoptera, but the more recent study, suggests that they are also close to the enigmatic Neuropterida, which includes many weirdos, some of which have featured on this site such as antlions, dobsonflies, lacewings and the platypus of the insect world, which we haven’t yet talked about (memo to self: must fix this), the mantisflies.
This means that the apparent developmental similarities between Strepsiptera and hemimetabolous insects is a product of convergent evolution. As the authors of the first of the two phylogenetic studies put it:
The striking similarity of the wing buds and complex eyes of the Strepsiptera late instar larvae to those of hemimetabolous insect nymphs suggests the reuse of a pre-existing developmental program (homoiology), possibly triggered by a simple change of developmental timing (heterochrony). Our analyses demonstrate that the development of wing imaginal discs and the absence of compound eyes in larval stages are ground plan features of the extremely successful Holometabola and that Strepsiptera are consequently not the “missing link” between hemi- and holometabolous insects.
Despite the fact that various aspects of their lifestyle can be creepy, these are truly amazing insects. You can even get them on a t-shirt! Here’s the design, by Ainsley Seago. At one point, you could buy it through Etsy…
h/t Mike Hrabar (@MikeHrabar) and Sean McCann (@Ibycter)
More on Strepsiptera here:
References
Boussau B, Walton Z, Delgado JA, Collantes F, Beani L, Stewart IJ, et al. (2014) Strepsiptera, phylogenomics and the long branch attraction problem. PLoS ONE 9(10): e107709. Here.
Hrabar M, Danci A, McCann S, Schaefer P, Gries G (2014) New findings on life history traits of Xenos peckii (Strepsiptera: Xenidae). The Canadian Entomologist FirstView: 1–14. Here
McMahon DP et al (2011) Strepsiptera. Current Biology 21:R271–R272. Here.
Niehuis O, Hartig G, Grath S, Pohl H, Lehmann J, et al. (2012) Genomic and morphological evidence converge to resolve the enigma of Strepsiptera. Current Biology 22: 1309–1313. Here
Wang, B. et al (2014) A diverse paleobiota in early Eocene Fushun amber from China. Current Biology 24:1606-1610. Here.
Such bizarre insects! I’d never heard of them before, despite being a bit of an ento-nerd myself! Thanks for sharing.
I propose that Strepsiptera evolved via a symbiogenetic mating event between a parasitoid wasp and a velvet worm. Someone write that up for PNAS.
This is seriously creepy. Just saying.
Wow! What a great post! Thanks very much again WEIT for constantly alerting us to the wonders of the natural world esp. insect!
Matthew – can you also ‘do’ Psocoptera some time? I just found one in a book (I twe#ted a pic)…?
What but design of darkness to appall?–
If design govern in a thing so small.
Robert Frost
Nothing constructive to add, just a placeholder to say that we do indeed read and enjoy (probably the wrong word in this case) the science posts.
Agreed.
Thanks for this wonderful post, Matt — food for lectures, for sure! Those videos are amazing.
These are not Godly creatures, these are of the Devil!
I agree, these are amazing animals ,though, of course, all are, everything is) and I’m so glad to learn about them. Love them parasites! Who needs miracles(or fiction) when such wild and crazy things are out there in the real world? In a Christian bestiary, they’d surely be branded as creatures that somehow sinned against God and so were punished by having to endure such a tortuous, not to mention torturous reproductive cycle.
And how about a post sometime on the marvelous cymotha exigua, the tongue-eating fish louse, perhaps my favorite parasite, just because — no more “cat got my tongue” blame it on a tongue-eating fish louse.
Also, a reminder the names of parasites are superb to hurl at people as insults, much more creative than the usual expletives, this evades opprobrium generated by simply calling someone a MF or AH, and sure to knock most recipients for a loop — tell ’em to go to Google. Louse is the least of them; great fun to call someone a nematode or a cestode; I’m searching for more. And though tube worms aren’t parasites, one should not forget gutless tube worms — a wonderful insult for a coward.
I love it. Hmm, not seeing a common name for this species, but “parasitic (because very few will know the diff between parasite & parasitoid) insect gut beetle (close enough)” sounds like a start. “You parasitic insect gut beetle!”
:–)
Thanks. That’s a good one. I can think of someone right now whom I’d like to call a parasitic insect gut beetle. More? For purposes of vituperation it doesn’t matter to me whether the beastie in question is a parasite or a parasitoid (which I hadn’t thought of); and in fact, invoking parasitoids can be even more apt in some circumstances when the person in question is destructive in the way parasitoids are.
😀
Who sez parasitology isn’t fun?!
Great post! Just when I think I’ve heard about the strangest insect behavior, something like this comes along. Those emergence videos are some serious nightmare fuel!
Peripheral comment: your survey of the neuropteroid taxa omitted two of my favorites: snakeflies (very common in California) and owlflies. Both are right up there in coolness with mantispids.
Ooh yes owlflies. We used to catch them on the field course I ran in the foothills of the French Alps. Snakeflies, not so much…
Like dudebros let loose on Ladies’ Night.
Mating, when it happens is joyless and brief.
Brief, indeed. But joyless? Who knows?
From the way the male was dancing in circles and came back for more…I was pretty sure I caught a glimpse of a smile.
Smiling the smile of the sated, the Strepsipteras light up a smoke.
“Did you feel the host move, too?”
(Ask not for whom the parasitoid tolls … )
Ah, others are there first… But from whose point of view is the mating ‘brief’? Since the males live only a few hours, the fraction of their lives spent doing what they are designed to do (Thank you, God, for Strepsitera!) is surely reasonably large, and perhaps larger, if someone were willing to try to work it out, than the fraction of their lives spent by human males doing what they are designed to do. No, joyful and protracted, surely, rather than joyless and brief!
The second video is amazing. I wonder if it is in “real time” or if it has been sped up. My guess is that it has, otherwise those mandibles are amazing! Snip, snip.
It does remind one of a cartoon character sawing through the floor in a circle around another cartoon character.
I checked with Mike Hrabar who confirmed that that video is soeeded up 2x – MC
I was jogging once and got something in my eye that caused severe, immediate irritation (no lasting damage). The tiny object that I removed with my fingertip turned out to be a strepsipteran.
Now that is a claim to fame! – MC
Was it in flagrante (albeit joyless and brief) delicto?
(The strepsiptera, I mean; you already said you were jogging.)
Spoken like a true biologist! 😀 Did you know it right off or have to look it up?
I was once dining in Costa Rica with a biologically-oriented friend when she dipped her spoon into her soup and came up two cockroaches. She holds the spoon out to me across the table and remarks, “that’s the family Blattidae, isn’t it?”
“Table for two for the Blattidae family …”
😀 Good one.
Like my bloody father. Now, I don’t mind him identifying sedges at 50 paces when we’re out for a walk. But it’s a bit disconcerting when he’s driving down the motorway at 90 and he’s looking at the plants on the bank of the opposite carriageway.
Sounds like a wonderful Dad.:)
And nearly as dangerous as we birders, driving along watching the sky…
They are indeed weird. I have had the privilege of seeing a couple females sticking out of the abdomen of a wasp. Never seen a male, however.
I think they were at some point put into the coleoptera, but I guess the consensus now is that they are a sister taxon. There are some very weird parasitic coleoptera, too.
Yikes, that is some amazing video work of this creepy insect. Its eyes look like caviar. I didn’t know anything about strepsipterans, so thanks for the post.
Looking forward to a piece on mantisflies.
Science, more amazing than science fiction. I can just imagine god having a sadistic chuckle as he creates these.
The eyes are intriguing – the Niehuis paper, as Matthew cites above, indicates that the complex eyes appear in the late instar larvae, and may be an example of heterochrony. I vaguely recall seeing images of compound eyes in mutant Drosophila strains that resembled those of the wild-type Strepsiptera, but can’t remember the genes involved. Now I’m wondering about the comparative genetics of eye development across insect orders ….
Very interesting. And creepy. (Comment to let you know I do read the science posts.)
Matthew’s postings are always illuminating and I have quite a few already in my #TIP http://www.tortucan.wordpress.com dataset. This one is especially useful on the systematic issues of how science ferrets out phylogeny based on close study of the developmental biology and detects the play of convergence (antievolutionists, especially ID advocates like Casey Luskin are especially obtuse on the convergence issue, so this will be helpful in contrasting how the actual scientists approach the data).
cs
Then the halteres possibly come from the Neuopteran side? Though IIRC the halteres of crane flies are derived from the second set of wings, like Dipterans, not the first.
What spectacular videos! A fascinating creature to know about! I’m curious as to what they dine on within their hosts that doesn’t result in killing it; especially when there can be more than one Strepsipteran larvae at a time within a host
Oooooh! I can just see the poor wasp going, “Ow! What the….OW! Ouch! Ouch!, what IS that…OW!”
Well like with all parasites, it would be deleterious for the host to kill itself too quickly (i.e. by being overcome with pain so it either doesn’t maintain itself or becomes food for something else). This is an organism which has been around for a very long time, so IMO the chances are good that the pain of the females subsisting on you is at least tolerable. Since the males fly away though…I’m not sure there would be any reason for any adaptation to evolve that would allow their ‘exit’ to be less painful.
That second video!!
Sharp and creepy. I’d have nightmares if these guys were larger and part of my day-to-day life.
Tangentially, makes me think of human embryos as parasites–a boring and old concept. But the birth images took me there.
“…makes me think of human embryos as parasites…”
They’re endoparasites for the first nine months, then ectoparasites for, oh at least 18-20 years or so, and sometimes for life!
Watching the emergence video … either there is some sort of membrane between the inner edge of the body-wall plate and the overlaying plate, or wasps (insects (arthropods!) in general have some pretty hefty immune systems to cope with whatever tries getting in between (not through) the plates.
Which in itself suggests targets for developing anti- arthropod/ insect/ wasp/ specific wasp chemicals. Not that pure research ever has potential pay off in real-world developments, oh no!