When it comes to finding the world’s most [insert adjective] insect, one usually needs to go to some remote, usually tropical location. But it just happens that the world’s smallest cricket lives right around the corner from my house.
The Eastern ant cricket (Myrmecophilus pergandei) is a remarkable and highly adaptable little creature. These insects are completely wingless and, unlike other crickets, do not produce any sounds; in fact, they don’t even have ears, which indicates the loss of sound production early in their evolutionary history. (And thus, do not believe what the Internet tells you – you cannot find them “by listing to the quiet ‘tweeting’ of the ant piles.”) Their size ranges from about 1.7 to 5 mm, making them the smallest members of the order Orthoptera. Ant crickets show a remarkable size polymorphism, and individuals of the same species can vary wildly in their body length, depending on the size of their ant hosts.
As their name indicates, these crickets are obligate inquilines of ants i.e., you will not find them outside of ant colonies, and they probably would not be able to survive in the open for very long. The Eastern ant cricket is not particularly host specific, and has been found in association with about a dozen of ant species; recently it has been recorded even from the nests of the invasive fire ant (Solenopsis invicta x richteri.) They are able to move among different ant colonies thanks to their ability to mask themselves by covering their bodies with cuticular hydrocarbons of their hosts, which the ants use as chemical signatures to tell apart their nest mates from enemies. But how do crickets acquire these compounds?
It turns out that upon entering a new colony the crickets must literally steal the hydrocarbons from the ants. They do so by sneaking up on their hosts and quickly rubbing their bodies against those of the ants. They have to be very careful though, because at this point they are still seen as intruders, and will be quickly killed if caught. This is when their huge jumping legs and incredible agility come in handy. They also scrape residual hydrocarbons from the walls of the colony and cover their bodies with it. Once properly camouflaged, the crickets are less likely to be molested by their hosts, and will even attempt to elicit feeding from ants by palpating the ants’ mouthparts. Interestingly, not all species of ant crickets are as flexible in their host choice as the Eastern ant cricket: some, like the Japanese M. albicinctus, require specific hosts and will perish if transferred to a different species’ colony.
A few days ago I went to a small wooded area near my house in eastern Massachusetts to look for ant crickets. I flipped a bunch of rocks, and eventually located a few individuals in the nests of two species of Formica. But I was surprised to discover that the ant crickets were not the only jumping guests of the ants. Another species of cricket, the Carolina cricket (Eunemobius carolinus), was present in nearly every ant colony that I looked at, and not only those of Formica, but also Aphaenogaster and Tapinoma. Carolina crickets are normally free-living insect, very common in my garden. I wonder if we might be witnessing the first stage of the process of a species becoming an ant symbiont, and if so, whether they use a similar chemical deception as that used by the ant crickets.