This Year, Why Not Zap Your Bad Garden Bugs with Good Ones?

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Robber flies can be recognized by their whiskered faces, long, spindly legs, and (usually) long abdomens. (Some have broad, hairy bodies and look very much like bumblebees.) Probably the only time you'll see these strong fliers is when they've landed on a leaf or stem to eat right after they've made their catch. On the menu: anything from grasshoppers, flies, beetles, dragonflies, bees, and wasps to the bumblebees these handsome insects mimic.

WASPS

Like the fly family, the wasp family contains both predators and parasites. Among the food insects that the large, predatory adult wasps catch to feed to their young are houseflies, blowflies, moth caterpillars, army worms, and corn earworms.

Aphids are also attacked by wasps, but in a different way: Watch an aphid colony long enough, and you're bound to see a very tiny female wasp carefully deposit an egg with her long ovipositor into the body of one of the little sapsuckers. When the larva hatches, it'll feed off its aphid host.

A variety of worms and caterpillars are also parasitized by wasps. If you happen to notice small, white, oblong objects on a tomato hornworm's back—for instance—you're looking at the cocoons of the braconid wasp's larvae. (Eventually, these cocoons will completely devour the hornworm.) Braconids also parasitize corn borers, various butterflies and moths, birch leaf-mining sawflies, wood-boring beetles, bark beetles . . . even ants. In every case, the parasitized pest insect is killed before it can do damage to its host plant.

Several species of tiny wasps are raised commercially for their pest control (i.e., parasitism) value. These wasps include:

TRICHOGRAMMA WASPS: Collectively, the various members of this group lay their eggs inside the eggs of more than 200 insect pests, including those of bollworms, leafworms, fruitworms, cutworms, army worms, cane borers, and most moths and butterflies.

FLY PARASITES: Maggots are the target of this group, which means that feedlots, poultry ranches, dairies, animal pens—anyplace where the common fly breeds—can benefit from having these parasitic wasps around. (It is estimated that the wasps in this category can destroy up to 95% of the developing maggots in a given locale in one season.)

SCALE PARASITE: This extremely tiny wasp (species designation unknown) lays its egg right under the scale that scale parasites secrete to protect themselves. The developing wasp larva then attacks the scale insect's body directly. Although this wasp primarily parasitizes the California red scale, it'll also attack a number of tree-loving scale insects.

SPIDERS

Though they're technically arachnids, and not insects, spiders are—nonetheless—probably the most important "biological control insects" you'll find in your garden. Like mantids, spiders will adapt to a variety of settings and feast on just about every kind of insect that happens by.

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