This silverfish didn’t fool the army ants. But many do.
The silverfish Malayatelura ponerophila is a kleptomaniac parasite that lives amongst the fierce army ants of southeast Asia, hanging out in the insect’s mobile colonies and living off the food they bring home. But how does it survive as a full-time impostor?
A study just accepted for publication in the journal BMC Evolution shows that these furtive freeloaders avoid detection by rubbing themselves all over immature ants called callows, “adolescent” ants which recently emerged from their larval stage. This gives the silverfish a coating of chemicals, called cuticular hydrocarbons (or CHCs), that the near-blind ants use to recognize nestmates in the dark. It is a dangerous way to live; army ants have keen senses and are usually adept at recognizing intruders, even expelling or killing fellow Leptogenys distinguenda if they smell like they’re from a different colony.
In the study, the researchers first catalogued all the cuticular hydrocarbons used by the ants, finding 70 in all. Doing the same for the silverfish, they found it made none of its own. They then coated the immature ants in a radio-labeled hydrocarbon similar in structure to others CHCs. They found that the silverfish acquired high levels of this marker after a day spent in close proximity to the callows, which they could be seen rubbing against from time to time. Poor callows—ant tweens old enough to smell right but too young to know the difference between a healthy attena-tap from a nest-mate and the silverfish’s unwanted rub-down.
In a separate experiment the researchers also isolated silverfish for about a week, and found that levels of these ant-smelling chemicals gradually decreased. They then compared the interactions of army ants with isolated and non-isolated silverfish. As predicted, the ants responded more aggressively to the isolated parasites, snapping at or attacking them about five times more often.
If the results stand up, it will be the first demonstration of an ant imitators acquiring all of its CHCs from the ants themselves. Several other types of so-called myrmecophiles have been show to synthesize chemicals in order to blend in.
Surprisingly few of the silverfish were actually killed in their interactions with ants (contrary to the suggestion of the above photo); 75 percent of the isolated creatures survived despite frequent attacks. The researchers speculate this may be due in part to the silverfish’s quickness, as well as its short appendages, retractable head, and scaled, drop-shaped body. This shape has been seen in unrelated myrmecophiles, suggesting it’s a good way to go if your lifestyle may lead to frequent attacks from groups of ants.
Reference: Christoph von Beeren, Stefan Schulz, Rosli Hashim and Volker Witte. Acquisition of chemical recognition cues facilitates integration into ant societies. BMC Ecology. 2011. DOI: 10.1186/1472-6785-11-30
Image credits: Christoph von Beeren.