"So, naturalists observe, a flea has smaller fleas that on him prey; and these have smaller still to bite ’em; and so proceed ad infinitum."
- Jonathan Swift

September 6, 2015

Chordodes formosanus

For most insects (and other small animals), the praying mantis is a creature out of their worst nightmare; a deadly predator with giant compound eyes, a nasty set of high-speed spiky grasping limbs, and an appetite to boot. But Chordodes formosanus is a parasite that would give mantis nightmares - it is a hairworm - and regular readers of this blog will know immediately why that is justified.
From Fig. 2 of this paper
The worm starts out as a microscopic larva hidden inside the body of small insects - the mantis' usual prey - but once it is ingested by a mantis, it can then grow to several centimetres long inside its abdomen. By the time it is ready to bid farewell to its reluctant host, which comes when it reaches sexual maturity, the worm has already taken up most of the space within the mantis, leaving it a half-empty husk. The modus operandi of a horsehair worm is to then get into the water, which involves the host taking a dunk - whether it wants to or not. Apart from commandeering the mantis to go for a terminal end to their relationship, during the worm's development, it takes a massive toll. After all, one does not simply host a giant worm inside one's abdomen without any consequences.

But the said consequences is not equally distributed within the mantis population - this hairworm seems to affect male mantis more severely - especially in regards to their reproductive capacity. In a nutshell - C. formosanus shrink their testes and in some cases, they disappear altogether. However, this parasite seems more forgiving when it comes to female mantis; infected female mantis can harbour the worm and still retain intact reproductive organs. Not to say it doesn't exact a toll, just that the female mantis can still have some babies before her end comes. So why this sex bias? The reason lies in how this parasite alters the host's physiology.

When researchers looked at various aspects of the infected mantis' physical appearance, they also noticed some external changes in both sexes - they had comparatively shorter walking legs, smaller wings, and altered antennae - but it was more pronounced in the infected male mantis. Overall, the infected individuals have an appearance which bears closer resemblance to that of late-stage juvenile rather than adults. This suggest that C. formosanus might be tempering with the mantis' so-called "juvenile hormones" which control development in insects. But why is it that only the male mantis lose their reproductive organs? At this point, it is not entirely clear, but it might have something to do with the different role played said hormones in the development of each sex.

So why has C. formosanus evolved to castrate their male mantis host? From the parasite's perspective, host castration is a very effective strategy - the host does not need its gonad to survive, only to reproduce. So by tapping into this energy source, the parasite can keep the host alive while maximising the amount of resources it draws from the host.

For that, the host pays a double cost in terms of evolutionary fitness. Usually with such parasite infection which inevitably results in the host's death, the best thing for the host to do to make the best of a bad situation and reproduce as much as possible before they are eventually killed by the parasite. But in this case, the male mantis doesn't even get to do that - thanks to C. formosanus, long before it bid farewell to life, it has to bid farewell to its junk as well

Reference:
Chiu, M. C., Huang, C. G., Wu, W. J., & Shiao, S. F. (2015). Morphological allometry and intersexuality in horsehair-worm-infected mantids, Hierodula formosana (Mantodea: Mantidae). Parasitology 142: 1130-1142

33 comments:

  1. Though the killing of the mantis in this video is abhorrent, the 'escaping' parasite is fascinating: https://www.youtube.com/watch?v=bcj0Srt8i6k

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  2. Left unsaid, but probably the likely outcome of being castrated is that the male mantis also never attempts to mate. Without the gonads, there is nothing to produce the hormones I imagine to properly tune the male to respond to a receptive female.

    The benefit to the ADULT hair worm is likely it avoids sharing the almost certain death of a male mantis during mating as many allow themselves to be eaten during the mating process to ensure maximum success.

    As a developed hair worm, it cannot escape being killed when eaten as its entire exoskeleton would be destroyed by the mantis jaws, nor can the undeveloped eggs infect her.

    Since the female mantis does not share that fate, the worm has not needed to develop a strategy to counter the mating process in infected females.

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    1. Perfect theory, which I suspect is exactly the case.

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    2. And silly me was here thinking it's pretty much easier to get a person to do what you want if you have them firmly by the balls.Thanks for this. Sounds so much more logical.

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  3. Is it a danger to humans?

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  4. Could it cause danger to animals? (If a cat or dog etc. were to eat a mantis)

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    1. No, it wouldn't cause any danger to them. The adult worm is essentially an aquatic animal and it cannot survive inside the gut of a mammal (it'll probably just get digested)

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  5. what happens to the parasite after leaving the mantis?

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  6. Eewww. Gross. Nasty. Ugh. Yuck. Nature is so gruesomely disgusting sometimes.

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  7. Wow how sad this is such a helpful insect too.

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  8. We love preying mantid in our house! How does the worm compel the mantis to take a swim? It sounds like it needs a water birth.

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    1. Hairworms are well know for compelling their insect host to jump in water bodies to give it a "water birth" since the adult need to be in water to reproduce. As for how they actually control the host's behaviour, that's still being figured out by researchers, but it seems to be based on some molecules secreted by the worm that affects the insect's nervous system.

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    2. If I recall correctly, it releases a protein that drives the praying mantis insane and gives it the urge to drown. I believe the Cordycepts fungus' ability to control the mind of an ant works off the same principle.

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    3. The worms make the praying mantis suicidal.

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    4. Saltwater or fresh water? Isn't there a chance that the bug would be eaten by a fish or frog the minute it hits the water?

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    5. The adult escapes into freshwater - hairworms like this have also evolved a way of escaping from the mouth of any fish or frog that ate the insect they are trying to escape from. See:
      http://zoo.unibas.ch/people/david/Ponton_parasito_2006.pdf
      and
      http://zoo.unibas.ch/people/david/Ponton_nature_2006.pdf
      and this video: https://www.youtube.com/watch?v=OUNaHEjaZ74

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  9. I think it basically takes over the praying mantis and puts it in a sort of zombie-like state.

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  10. Alien Covenent was less disturbing than this... Seriously, nature is just so fu**ed and people say a kind loving God creates such horrible things.

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    1. Everything on earth has a purpose. Just because it freaks you out does not mean nature is fu**ed and as far as God is concerned, kind and loving has nothing to do with how we all need to survive and that includes worms.

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    2. No such thing as God

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    3. Maybe not for u... but there's a God.

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  11. WHOA�� MIND BLOWN

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  12. Is it possible for the mantis to survive once the worm has been removed?

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  13. I’m trying to figure out why I have found 2 praying mantis within the last 2 weeks, and BOTH have died because of this hair worm. Can a local infestation be the cause? It’s quite worrisome.

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  14. How do I know if my mantid has a parasite? I got it from my garden when it was still at a young age,pretty much half the size of my thumb. So is it affected or nah?

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  15. My kids mantis is eating another Mantis like right now and a worm just fell out of the one she's eating. Just freaked me out which led me to this blog

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