We count on native pollinators for food: 35 percent of our crops do not set seed unless an insect or other creature transfers pollen from flower to flower. And among pollinators, the most efficient species are bees. European honeybees provide this service for many food crops, but it is primarily the roughly 4,000 species of bees indigenous to North America—including this yellow bumblebee—that sustain the native plants that run our ecosystems. Although indigenous species aren’t affected by colony collapse, landscaping practices that favor huge lawns and limited plant diversity have sent nearly all of our native bees into serious decline. Gardeners can help reverse this trend by growing flowers that provide pollen and nectar from April through October.
Because nonnative mantids from Asia and Europe are so common in North America, few people realize that we have 18 mantid species of our own, many of which spend their time hunting arthropods on the ground or on tree bark. Our most common and largest native species is the Carolina mantid, which, at 2 inches, is half the length of the Chinese mantid. Mantids are generalist predators, but they do not eat motionless aphids, scales, or caterpillars. Instead, they are attracted to moving targets, including garden pests like leafhoppers, earwigs, and cucumber beetles.
Named for the see-through patches on their wings, snowberry clearwings are one of several species of sphinx moths that look and act more like hummingbirds than insects. They are often seen hovering, like those diminutive birds, in front of flowers. A snowberry clearwing inserts its long, hollow “tongue” deep into the corolla of phlox and other flowers whose openings are too slender for most other insects. With this strawlike appendage, it sips the flowers’ nectar—and in the process, it picks up thousands of pollen grains and carries them to the next flower.
Bird lovers, take note: Without caterpillars, we would have few feathered friends. Caterpillars, the immature stages of butterflies and moths, get a bad rap as garden pests. But only a few species eat our crops, and even fewer favor our ornamentals. Most of the 14,000 species in North America, like the luna moth larva shown here, make their living harmlessly and unnoticed on wild plants. Ninety-six percent of our terrestrial bird species rear their young on insects, mostly in the form of caterpillars. These soft-bodied larvae—particularly the spineless and hairless ones—are ideal food for baby birds. They are packed with protein and lipids, and full of essential carotenoids, the antioxidants that create colorful feathers—a signal, in turn, of good health and diet. Birds that feed their nestlings caterpillars need many thousands of them to bring a clutch to the point where the young can leave the nest. Want to lure birds to your yard and help those youngsters to fledge? Plant native trees like oaks, which support the growth and reproduction of hundreds of species of birds’ favorite food.
Bees are typically far more effective pollinators than flies, but syrphid hoverflies are an exception. The 870 species of hoverflies in North America are so named for their habit of hovering for several seconds in front of flowers before they land. They have remarkable flight abilities, moving forward, backward, up, and down with ease. Their frequent visits to flowers result in the pollination of many plant species; fall-blooming plants like witch hazel depend almost entirely on hoverflies. Even as larvae, they’re beneficial; the immature hoverflies are voracious predators of aphids.
Crickets and other so-called detritivores are the unsung heroes of nutrient cycling. When plants or plant parts die and fall to the forest floor, they form a layer of detritus that nourishes the next generation of plants. The nutrients, however, are bound up in a matrix of cellulose that is difficult for living plants to access until it is broken down by other organisms. Among the many species of litter-dwelling detritivores, crickets, such as the field cricket shown on this page, are the largest and most apparent. Although we are accustomed to hearing their nocturnal chirps in late summer and early fall, when most cricket species mature, some species come of age as early as May. We can maintain crickets in our landscapes—and the healthy soil ecosystems they help to create—by leaving a layer of leaf litter as mulch in garden beds throughout the year.
Known as the sharks of the insect world, robber flies are powerful predators. They dart out from perches and catch grasshoppers, dragonflies, wasps, and even tough Japanese beetles as they fly by, subduing their victims with paralyzing venom injected via short, stout mouthparts. They’re far more common, though, than sharks; there are 7,000 species worldwide, distinguished by large eyes and moustachelike bristles on their faces. Some look remarkably like bumblebees, though they can be recognized by their two wings, rather than four. Make robber flies welcome in your garden with a couple of well-rotted logs; many species develop as larvae in such logs, where they prey on wood-boring insects.
From the moment they hatch until their deaths several months later, assassin bugs earn their name. They’re able to eat many types of insects, including caterpillars, Japanese beetles, and stink bugs, by using their sucking mouthparts to pierce the soft areas between the segments of their victims’ hard exoskeletons, then sucking up the liquid innards. Some species of assassin bugs coat their forelegs in pine sap to help them grip their prey. The wheel bug shown here is the largest species of assassin bug in the United States, reaching up to 1½ inches in length.
Mayflies develop in streams and lakes, where their larvae graze on algae and are eaten, in turn, by larger insects and fish. When they mature, most species emerge in swarms, millions of adults spreading large, diaphanous wings in a synchronized spectacle. These mass flights play a crucial role in nutrient cycling between aquatic and terrestrial ecosystems. Fresh-water habitats are under constant threat of eutrophication, or over-enrichment. With every rainfall, nitrogen, phosphorus, and other nutrients leach from the land into nearby streams and lakes. The soil ends up depleted, while the water suffers algal blooms and organic buildup. But when millions of short-lived mayflies flee the water to die and decompose in nearby woods and fields, they return nutrients to the soil. Thus the annual flight of mayflies lengthens the life of our waterways while fertilizing plants on land.
Extraordinarily numerous and ubiquitous, parasitic wasps help keep other insect populations from exploding. They range in size from less than a millimeter in length to 6-inch giants like the Megarhyssa ichneumonid shown here. As a group, parasitic wasps attack nearly every type of insect but are particularly effective at holding aphids, mealybugs, and caterpillars in check. Many have fascinating ways of increasing their numbers. One species lays a single egg within its victim, which divides into many eggs—sometimes thousands—that hatch and devour their host. Most adult parasitic wasps drink lots of nectar and will travel distances to find it, so a good way to attract them is by growing a diversity of flowering plants all season long. Look carefully within blooms: The tiny black insects deep in the flower, often no larger than a period, are the wasps that are keeping your yard’s ecosystem in balance.
The world’s largest family of flies, tachinidae includes well over 10,000 species. Many of these look like bristly houseflies, and all of them are parasitoids. Unlike true parasites, parasitoids kill their hosts, and in this way, they help keep garden pests in check. Although a few species attack scorpions, spiders, or centipedes, the vast majority of tachinids target insects—especially caterpillars. There are myriad methods of attack. Some tachinid flies lay eggs on vegetation that’s being eaten by a caterpillar, who accidentally ingests the eggs, which hatch inside its body. Some species inject eggs directly into a caterpillar using a specialized organ called an ovipositor, while others cement eggs near a caterpillar’s head in positions that make them impossible to scrape off. When the eggs hatch, the larvae tunnel into the caterpillar’s body. And tachinids that attack katydids and crickets track down their prey at night by following their mating calls. As with other beneficial insects, tachinids are very susceptible to pesticides; thoughtless spraying, even of organic products, often kills them.