Wait - don't step on that!

Most people scream at them, squash them, or spray them. They bug us.

But without insects, ecosystems on land would fall apart. Eliminating even a few species would wreck key parts of the web of life. It could mean much less pollination of plants, less food for other animals, and slower disintegration of dead organisms. Case in point: Of the 775 tropical plants that humans eat, 88 percent are pollinated by insects.

In "What Good Are Bugs?" Gil-bert Waldbauer, professor emeritus of entomology at the University of Illinois, gives us a bug's-eye view of the world with the intimacy of someone who gets inside the heads of these tiny, crucial creatures.

Known for several other books on bugs, including "Insects Through the Seasons," Waldbauer writes respectfully and almost lovingly about his "extended family," including their history, habits, benefits to the environment, and even eccentric behaviors.

For example, some ants essentially domesticate certain caterpillars that secrete a sweet liquid, the ant equivalent of a hot-fudge sundae. They even build shelters on the ground, much as humans do for cows, to keep the caterpillars safe.

Other insects possess astounding anatomical features, like the hawk moth in Madagascar that has a 10-inch tongue, much longer than its own body, but just long enough to sip nectar from white honeysuckle flowers. Watching the moth almost as large as a hummingbird poke into the flower without landing on it, Waldbauer comments with a degree of awe, "This was a critical moment for both plant and insect, an indispensable prelude to their ultimate goals, in both cases the production of offspring that would survive them and pass their genes on to future generations."

We are familiar with the more usual beneficial behaviors of insects, such as bees and other insects that pollinate flowers and spread seeds. But insects also aid in decomposing dead animals or droppings. Waldbauer points to a case in Australia, where the droppings of cattle were slow to decompose and choked off plant growth. Dung beetles imported from Europe finally helped solve the problem.

Insects also can defend plants, as Waldbauer discovered the painful way. As he was collecting insects one hot day in southern Mexico, he brushed lightly against a small tree. "Almost instantly a horde of small ants swarmed onto my bare arm and stung me ferociously," he writes. Waldbauer later found out that such ants can smell a person, cow, or other potential invader, and prepare themselves to sting anything that might threaten their tree.

Other insect anomalies include the fact that many insects would rather starve than eat anything besides their favorite plant. Male wasps can be so attracted to pollinate some species of orchids that they even try to copulate with flowers that look and smell like female wasps of their same species.

Most adult insects have similar anatomy, with bodies that consist of 18-19 segments in three groups: the head, thorax, and abdomen. Like humans, they also have five senses. They rely mostly on vision and smell to find flowers. And their senses of taste and smell are much more important to them than to humans.

Waldbauer aptly points out that while insects can both help spread plants and keep them under control, they themselves also are kept in check, sometimes brutally, by nature. For example, one night about 8.7 million bats left Carlsbad Caverns in New Mexico and ate 115 tons of insects.

Readers caught in Waldbauer's web of passion and amusement will appreciate the book's extensive list of selected readings, detailed index, and black-and-white drawings throughout. Besides providing a wealth of scientific knowledge on the history and activity of various insects, "What Good Are Bugs?" is a book accessible to lay readers, too. It helps bridge the love-hate relationship most of us have with insects, giving us a new appreciation for the way they creep through our lives.

• Lori Valigra is a freelance writer in Cambridge, Mass.