Eggs scramble: fungi trick termites into babysitting.

In a novel case of egg mimicry, a fungus is taking advantage of hard-working termite nursemaids, a researcher says.

A fungus in the genus Fibularhizoctonia forms compact balls of tissue that, under the right conditions, can start a new colony of the fungus, explains Kenji Matsuura of Okayama University in Japan. Termites in both Japanese and American species pick up these balls and tuck them into a nest's egg pries.

At first, Matsuura and other entomologists had speculated that fungi and termites both benefit from their relationship. Now, the fungi look as if they're just parasites, Matsuura says in an upcoming Proceedings of the Royal Society B.

The most famous egg parasites are birds. Cuckoos and cowbirds, for example, sneak their eggs into the nests of other species. The victims often accept an interloper egg and raise the chick.

The fungus balls are brownish spheres that don't look like the white, sausage-shaped termite eggs. However, it's dark in a termite nest. Mimicry doesn't have to be visual, says Matsuura.

He reports that some Reticulitermes-termite nursemaids adopt fungus balls that match the diameter of eggs. The fungus balls of this species are smaller than those of other species. In experiments with glass beads, he found that an object had to also have the right egg scent to appeal to the termites. Moreover, microscopy showed that fungus balls in this species have smoother surfaces, more like those of termite eggs, than do similar structures of closely related fungus species.

Matsuura also examined whether termites benefit from the relationship. His original research, conducted with two colleagues, suggested that more termite eggs survive if they commingle with fungal balls. But that study was conducted in a lab setup without natural nesting material.

Now, Matsuura has tested termite-egg survival in nurseries furnished with a chunk of wood plastered with termite droppings, which carry natural antibiotics. In this setup, Matsuura saw no jump in survival for eggs sharing a nursery with fungal balls.

He suggests that in the wild, termites waste energy on faux eggs made of a fungus that the insects don't eat. He points out that workers often groom more than 10,000 eggs and fungus balls per day.

Benefits in a mutual relationship, as well as costs, can take a while to tease out, notes microbial ecologist Cameron Currie of the University of Wisconsin-Madison. A benefit might show up only under certain conditions, so he says that he's looking forward to more research before declaring this fungus-termite relationship straightforward parasitism.

In any case, Currie says, "it's another cool example of an insect-microbe interaction."