Thirty percent of all animals on Earth are beetles with 34 times more beetle species than bird species. Within this immense order of insects (Coleoptera) is the family Chrysomelidae, the leaf beetles. It is a family of much interest to farmers and gardeners, as leaf beetles are very good at eating plants.

The list of leaf beetles includes the Colorado potato beetle, the cereal leaf beetle, the asparagus leaf beetle, the flea beetles that perforate the leaves of broccoli and eggplant, and the viburnum leaf beetle, a European beetle that has severely limited the use of several native viburnum species in Maine gardens. The most devastating species have been introduced to our gardens from other regions of the world.

Take the lily leaf beetle, for example. Native to Europe, it was discovered near Montreal in 1945. For decades, its damage was limited to the Montreal area, but in the summer of 1992 it was discovered in Cambridge, Mass., apparently entering the U.S. with bulbs shipped from Europe.

Lily leaf beetles are now devouring lilies in Maine gardens at least as far up the coast as Lamoine, where this past weekend I found them in a friend’s garden. Lilies are their preference, although they will nibble on Frittillaria, Solomon’s seal, potato, hollyhock, hostas and flowering tobacco (Nicotiana). They lay eggs, however, only on true lilies (Lilium). Daylilies (Hemerocallis) are safe.

The adult is a striking creature about 1/4-inch in length with a shiny scarlet body, black head and legs. They squeak when you squeeze them, a defense mechanism to deter predators.

Don’t let the squeaking deter you from hand-picking them off of your plants, preferably in the early morning while they are sluggish. Either crush them or throw them into a jar of soapy water, just like you treat Japanese beetles. Like the Japanese beetle, lily leaf beetles are able fliers and some will escape, perhaps to the neighbor’s garden.

The larvae resemble slugs with swollen orange, brown, yellowish, or greenish bodies and black heads. To deter their predators, including gardeners, they secrete and carry their excrement on their backs.

The adults spend the winter in soil or plant debris, often some distance from their host plants. They emerge from late March through June, mate and the females lay their reddish-orange eggs on the underside of leaves in an irregular line. The adults I found this past weekend were busy at these activities, so now would be a good time to inspect your lilies for eggs and either crush them or remove and burn the affected leaves. The window is narrow, however, as the eggs hatch in seven to 10 days.

The larvae feed on the underside of the leaves for up to 24 days and cause more damage than the adults. They can be hand-picked if you are not squeamish, or you can wear gloves.

The larvae pupate in the soil. After 16 to 22 days, new adults emerge and feed until fall; they do not mate or lay eggs until the following spring. Look for these new adults and eliminate as many as possible.

Neem oil, an insecticide based on extracts from seed of the neem tree, is the chemical of choice for repelling adults and killing larvae. Most effective on young larvae, it should be applied every five to seven days after egg hatching. Neem can be purchased under several trade names, including Turplex, Azatin EC, Margosan-0, Align and BioNeem.

University of Rhode Island scientists are working on biological controls for the lily leaf beetle, concentrating on parasitoids that control its populations in France and Switzerland. They hope to eventually release an effective control agent in this country.

Meanwhile, the presence of the lily leaf beetle gives us another reason to stay in the garden, keeping watch.

Send queries to Gardening Questions, P.O. Box 418, Ellsworth 04605, or to rmanley@ptc-me.net. Include name, address and telephone number.