Butterflies in their stomachs.

Among butterflies, the madrone species (Eucheira socialis) is a true oddball. For starters, this rare, mostly black insect inhabits just five species of madrone trees in the pine-oak forests of the Sierra Madre Occidental and the Trans-Neo-volcanic Moutains of Mexico. Second, its larvae forage together in a quasisocial manner atypical of butterflies. And third, the silk cocoons of larvae and pupae that hang on madrone trees in springtime -- as many of 20 bags per tree -- consist of unusually tought, double-stranded silk threads.

But those features aren't the only reasons why ethnobotanist Robert A. Bye has returned year after year since the mid-1970s to a forested site in northwest Mexico to study the madrone butterfly.

His research took wing in a forest just east of the town of Creel, Mexico, a popular madrone haunt. Bye discovered that the native Indians there have a long-standing tradition of eating the fatty, protein-rich madrone pupae, which they call iwiki. Roasting hundreds of the pear-shaped butterflies-to-be over an open fire and sometimes mixing the crisped pupae with corn gruel, some of the Tarahumara Indians appear to use the cooked materials as a nutritional supplement in late spring -- traditionally a time of food shortage between the end of the dry season and the beginning of the main agricultural cycle, Bye says.

Native people in Mexico occasionally eat some 100 types of insects, but snacking on madrone pupae now appears limited to elders in the Tarahumara tribe, observers Bye, director of the botanical gardens at the National Autonomous University of Mexico in Mexico City. Nonetheless, the practice -- though beneficial to the Tarahumara -- would seem to spell trouble for the butterfly, already threatened by lumbering of its pine-oak habitat.

However, Bye and his colleague, Peter G. Kevan of the University of Guelph in Ontario, found evidence that some tribe members practice animal husandry, taking cocoons from madrone trees that contain many of the silk bags and retying them with leather straps on trees that lack them. In this way, members of the Tarahumara may promote repopulation of the butterfly, Bye speculates. He adds that the redistribution of cocoons has only been found at sites where people eat the pupae.

This gustatory tradition suggests another line of research, Bye notes. Since madrone caterpillars munch on leaves containing glycosides -- potent chemicals that can affect the heart and are considered poisonous to humans -- he plans to investigate whether the larvae or pupae partially neutralize the chemicals. Cooking the pupae may also detoxify them, Bye says. He adds that Tarahumara members who eat large numbers of the pupae sometimes vomit or develop headaches.

Historical literature as well as recent interviews reveal that the silk cocoons of the madrone have served the tribe well as durable bandages, containers and flags, Bye says.