Lacewings have their armor and eat it too.

Some green lacewing mothers produce an unusual compound that both protects their eggs from marauding ants and serves as their offspring's first meal, researchers say. Someday, the chemical may enable humans to repel ants too. Before depositing their eggs, green lacewings release from their reproductive glands a substance that forms stalks for their eggs to sit on, keeping them out of the way of hungry predators.

One species of green lacewings takes an additional precaution, however. Ceraeochrysa smithi females produce droplets of an irritating fatty liquid that they deposit on the stalks to repel invaders, assert Thomas Eisner of Cornell University and his colleagues. Moreover, when the larvae emerge from the eggs, they imbibe the liquid. This snack may provide them with nutrients or make them less attractive to ants, the team speculates.

Many species of insects protect their eggs with chemicals, but scientists have found no others whose offspring ingest the defensive substance, the team contends in the April 16 Proceedings of the National Academy of Sciences. "As an insectan 'mother's milk' that seemingly combines the attributes of 'guns and butter,' the egg-stalk fluid of C. smithi is evidently unusual," they observe.

"It's a surprising and very interesting finding," agrees entomologist Charles S. Henry of the University of Connecticut in Storrs.

The researchers first noticed the droplet-covered stalks in the late 1960s, but they put their discovery on the back burner until better techniques for extracting the oil and examining its ingredients came along, explains Eisner. They found the stalks in Florida on palmetto fronds and on the leaves of a creeping fig tree.

Recent analysis with gas chromatography reveals that the stalk fluid consists primarily of concentrated fatty acids that make other insects itch. It also includes trace amounts of aldehydes, volatile chemicals commonly found in plants. Although another team reported recently that wasps impregnate their nest stalks with similar fatty acids to deter ants, few other insects' defensive juices have any of the green lacewing's ingredients, Eisner says.

He and his coworkers also compared how ants respond to the egg stalks of C. smithi and to those of C. cubana, which have no protective fluid. "In not a single test were any of the C. smithi eggs taken by the ants," they report. "Upon touching a stalk, ants abruptly backed off." In contrast, ants stole two to four of C. cubana's five eggs during each of the five tests. When removed from the stalks, both species' eggs got snatched with equal regularity.

Eisner plans to test how well the oil works against ants in a regular kitchen. When the scientists put a drop of a synthetic version of the compound on cockroaches, the bugs began scratching themselves within 3 to 6 seconds. He doubts the chemical can scare off the hardy cockroach, however.