Bay leaves may make rat nests nicer. (Biology).

A study of wood rats' housekeeping suggests they use pest control in their homes, too.

Dusky-footed wood rats (Neotoma fuscipes) along the west coast of Mexico and the United States leave nibbled bits of bay leaves around their sleeping chambers, explains Richard B. Hemmes of Vassar College in Poughkeepsie, N.Y. He and his colleagues report in the May Behavioral Ecology that their lab tests show that the bay leaves can kill flea larvae. The leaves might provide home fumigation, wood rat style, the researchers speculate.

When building homes, dusky-footed wood rats heap sticks into protective piles that may reach several feet in height and width. Inside, the rats tunnel and make several chambers, one typically cushioned with moss and chewed twigs for sleeping and others for larders and a latrine. This stickhouse can shelter one occupant after another for decades.

Hemmes and his colleagues surveyed stickhouses in Sonoma County, Calif. Many had the aromatic leaves of California bay plants around the edges of the depressions in which the animals sleep, whereas other types of fresh leaves tended to turn up in the other chambers.

The researchers tested fumigation power by incubating bay leaves in jars with flea larvae. Only about a quarter of the larvae survived 3 days with bay leaves, but more than three-quarters survived in leaf-free jars.

Ornithologists have reported that some birds, such as European starlings, tuck aromatic leaves with pest-fighting properties into old nests. However, says Hemmes, "this is the first report that we know about of nest fumigation in mammals.--S.M.