The moth Cosmosoma myrodora, pictured, is visually striking. And, as revealed by William E. Conner and colleagues in the Proceedings of the National Academy of Sciences USA (97, 14406–14411; 2000), its behaviour is also rather unusual. The male moths seem to have developed a chemical system to protect themselves, their female mates and their offspring from predation by spiders.
Conner et al. provide evidence that male — but few female — C. myrodora feed on the fluid secreted from certain plants (perhaps Eupatorium capillifolium). The alkaloid compounds thus ingested become particularly concentrated in a mass of filaments (pictured right) in the abdomen of the moths. The authors assume that this protects the males from spiders such as Nephila clavipes — when the moths were fed a similar alkaloid in the lab, the spider cut the moths free from its web rather than eat them.
Before mating, male C. myrodora release some of their filaments, covering their chosen female. This seems to protect the female from spiders, too. The females may also receive alkaloids from the males' sperm, and in turn pass on some of these protective chemicals to their eggs.
But questions remain. Do the females use receipt of alkaloids as a measure of a male's 'worth'? Females did seem to prefer males that had released filaments, but it is not certain if females could discern whether the filaments were laden with alkaloids. It is also not clear which plants the moths feed on in the wild, because the moths are rare and hard to spot.