"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

November 6, 2016

Macrodinychus multispinosus

There are variety of mites which live with ants, but many of them are not well-studied. Most of them are either phoretic mites which hitch a ride on the ant's body, or detritivores that eat various substances which can be found in ant nests and in those cases, they are relatively harmless commensals. But some mites that live with ants are ectoparasites. The study being featured today is about a mite that lives (and feeds) on ants - Macrodinychus multispinosus. There are variety of other mites that also feed on ant haemolymph (a fluid which is the equivalent of blood in insects), but this vampire takes it to an another level.
Left: Ant pupa host being progressively eaten alive by the parasitoid mite.
Right (top): Adult female and male Macrodinychus multispinosus mites
Right (bottom): A M. multispinosus nymph at the stage when it is attached to the host (note the stumpy legs)
Photos from Figure 1, 3, and 5 of the paper. 
Newly hatched M. multispinosus nymphs are born with fairly long limbs which allows them to move about and find a host, but once they are attached to an ant pupa, their limbs are reduced to stumps. The mite essentially become a tiny biological pump. And whereas other blood-sucking mites that feed on insects are content with imbibing just some of the host's life blood, M. multispinosus does not hold back - it consumes all the developing ant pupa's internal tissue and literally sucks the life out of it.

Macrodinychus multispinosus can be considered as a parasitoid - even though its modus operandi is very different to parasitoid wasp which devour their host alive from the inside and burst out xenomorph-style once they are ready to pupate, the outcome is pretty much the same - a dead, empty host. The researchers behind the paper being featured in this post conducted their study at Quintana Roo, Mexico across a number of field sites where they inspected colonies of the longhorn crazy ant
(Paratrechina longicornis) - the mite's only known host.

They found this vampire mite to be relatively common - of the seventeen colonies they sampled, eight of them were infested with M. multispinosus. Overall, about a quarter (26.2%) of the ant pupae they examined were infected with these mites. In some nests, over three-quarters of all the pupae are parasitised. They noticed that M. multispinosus definitely seems to have a preference for the worker ant pupae and developing queens are usually spared. Even though by doing so, this vampire wouldn't end up killing off potential future colonies by parasitising the reproductive members of the colony, it is still killing off the developing workers and this can be quite harmful at a colony level if the mites are present in high numbers.

It seems that M. multispinosus has settled quite well into its niche as a ectoparasitoid of the longhorn crazy ant, and like other mites in the Macrodinychus genus, it is rather specific about where it attach to the host - in this case the ant pupa's abdomen. But here's the twist - whereas M. multispinosus is native to Quintana Roo, its host is not and is a relatively recent arrival to the region. Even though this vampire mite must have been parasitising ants long before the longhorn crazy ant came along, its original host is still unknown to science - in fact, even though it was described in 1973, it wasn't until now that its ecology and life cycle has been documented.

There's still a lot to learn about this little vampire. Would it be a good biological control for the invasive longhorn crazy ant? What kind of ant did M. multispinosus originally parasitised before it jumped on the invader? How was it able to take to the newly arrived host so quickly?

With so many different kinds of organisms being transported (purposefully or inadvertently) around the world, perhaps is would be useful to consider recruiting parasites are as a mean of controlling invasive species, especially if the parasite is native to the region where biological control is being considered - that way, it'll be fighting on its home turf.

Reference:
Lachaud, J. P., Klompen, H., & Pérez-Lachaud, G. (2016). Macrodinychus mites as parasitoids of invasive ants: an overlooked parasitic association. Scientific Reports 6: 29995

P.S. If you like this post and other posts like it on the blog, then you might been interested in checking out the book "The Wasp that Brainwashed the Caterpillar" by Matt Simon. It is full of funny and informative stories about wonderfully weird and bizarre animals both parasitic and non-parasitic - you should totally check it out!

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