In the glossary at the end of Les Fourmis, Bernard Werber describes the staphylinid beetle Lomechusa strumosa as a "purveyor of deadly drugs" (Werber, 1991). During the course of the story, our formicine heroes encounter one such Lomechusa in the "basement" of the ant colony. According to the ants, "no sensation can equal that which follows the absorption of Lomechusa's nectar, once it has been tasted. Fruit of all physical desires, its secretion destroys the strongest wills" (Werber, 1991). Ants who have partaken of the beetle's offerings are described as junkies, forever in search of their next fix. Obviously, Our Heroes zap the unfortunate beetle with formic acid.To be pedantic, Lomechusa strumosa parasitizes Formica sanguinea and not F. rufa, the hero of the story. To be fair to Werber, it does make itself irresistible to ants, although its method is not addictive. It is counted among the many insects that have successfully cracked the chemical code of ant communication.
Picture of the beetle from here.
Lomechusa strumosa, and the closely-related Atemeles beetles, are highly advanced nest parasites of ants. They specialize in exploiting the brood chamber - one of the most heavily-guarded areas of the entire nest. Not only are the beetles allowed to live in the nest, but the ants also feed them and groom them, while the beetle's grubs munch unnoticed on the ant larvae.The secret of Lomechusa lies in its tactile and chemical deception. When faced by an ant, Lomechusa gently taps the ant's labium, inducing it to regurgitate food. The beetle's mechanical signals are the same as those used by the ant's larvae; however, they are more intense and "convincing". In fact, Lomechusa ends up being fed more than the ant larvae! (Hölldobler and Wilson, 1990).
Pictures above and below taken from here.
Lomechusa's chemical secretions are even more remarkable. Its abdomen houses an entire chemical factory, producing volatiles for all occasions. A repellent secretion is used to ward off non-host ants. In the presence of host ants, Lomechusa first entices the ants to lick the trichomes (glandular hairs) on its legs. It then presents the tip of its abdomen to the ants, which exudes an appeasing, calming substance. Finally, adoption glands down the sides of the abdomen are also exposed to the ants, and the beetle is picked up and carried into the nest.
Once in, Lomechusa never wants for anything. It is feed by the ants, and, in return, it lets ants have the occasional sip from its delicious secretions (which are not addictive, to the best of our knowledge). The fact that its behavior apes that of ant larvae means that the beetle gets fed the most nutritious food, destined for the brood (Hölldobler and Wilson, 1990).Lomechusa overwinters among the ants, with beetles dispersing for new nests during the summer. New beetle grubs are born in the brood chamber, and the grubs are fed by ants, who turn a blind eye when it wolfs down the ant larvae. When needed, a grub can secrete is own chemicals to ensure attention from the ants.
In short, Lomechusa has everything going for it - a sheltered environment, endless free food, and the protection of the most redoubtable insects in the woods. It may seem that they could effectively destroy an ant colony, but Lomechusa is its own worst enemy; its cannibal larvae will also eat other, thus limiting their own numbers (Hölldobler and Wilson, 1990).
Werber got one thing right - Lomechusa is a freeloader and a parasite that lives off ants. However, ants seem incapable of seeing it for what it is, its chemicals are soothing but not addictive, and, once in the nest, they don't leave the brood chamber.
References
Hölldobler, B. and Wilson, E. O. (1990) The Ants. The Belknap Press of Harvard University Press, Cambridge, Massachusetts
Werber, B. (1991) Les Fourmis. Editions Albin Michel.
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