New gardeners hear a lot about “beneficial insects” without realizing exactly what that term means. To scientists, all insects are beneficial in some way. Some are food for fish, for example. To gardeners it means only those insects that eat or parasitize insects that interfere with human activities. Some beneficials eat insects, others suck out the life juices of other insects.
Most gardeners are acquainted with Lady beetles or Lady bugs, those oval, hard-shelled little orange beetles with black dots and black heads, and regard them as valuable garden helpers. It’s actually the larvae of Lady beetles who consume the most aphids, but the parents eat some too. Both will also eat other small insects such as thrips, flea beetles, whiteflies and one another, like most carnivorous insects do.
Lady beetle larvae look like dull-coated tiny alligators, black with some orange spots. They’ve hatched from orange eggs, laid in a cluster on the undersides of leaves, long eggs standing on end. Squash bugs lay their orange eggs on the undersides of squash bug leaves. The differences in appearance are that the squash bug eggs are darker in color, rounder, and shinier than the Lady beetle eggs. The Lady beetle eggs look like bowling pins standing on end.
Keep the appearance of Lady beetle larvae in mind, for the lacewing larvae also look like tiny alligators, matte-finish, but these are pinkish-brown in color. Some may have brown and white marks on their bodies. Green lacewings lay eggs on sturdy silk stalks that stand up about an inch and a half above a leaf. They’re hard to see, but there may be several stalks, each with a single egg, on a single leaf.
Adult green lacewings only feed on aphids’ honeydew and nectar, but their larvae gobble loads of aphids, thrips, whiteflies, mites, and eggs of moths, cabbage loopers, asparagus beetles, corn earworms and possibly leaf miners. Their adult size is about three-eighths of an inch.
Some call lacewing larvae “ant lions,” and these may wait at the bottom of a funnel of fine soil, soil so fine ants and other crawling insects can’t get a foothold and slide to the bottom where the lacewing larva is waiting with open jaws.
Hover flies are numerous here also. They look like small bees, but frequently stop and hover over a plant. The adults need shallow sources of nectar, so they and the other tiny beneficial insects are especially drawn to clusters of tiny flowers such as yarrow, dill, parsley, agastache or Chaste tree blossoms.
Their maggots look almost like small slugs, and the pupas look like a tear-shaped blob. This is a beneficial creature too easy for a gardener to destroy, but shouldn’t. Other beneficial insects parasitize other insects by laying eggs in or on other insects or their eggs. If you see a tomato hornworm with what appears to be rice grains on its back, don’t kill it. Let the parasite larvae do that. There are parasites that attack squash bugs, but they look to the unmagnified eye like houseflies with orange abdomens.
Other beneficials in our area include wasps, spiders, preying mantises, Tachinid flies, Damsel bugs, minute pirate bugs, parasitic wasps (usually tiny, non-stinging), and predacious ground beetles. To attract and keep them around, provide a constant supply (overlapping blossom times) of tiny flowers with shallow nectar reservoirs; provide water in shallow birdbaths (water changed every couple of days to destroy mosquito larvae), or droplets on leaves; and use specific insecticides when you must, never broad spectrums.
Insecticidal soaps, horticultural oils (especially for scale), stomach poisons for foliar feeding insects, and Bacillus thuringiensis (BT) are deemed to be safer to beneficials than other pesticides. Always read the label. Does your chosen pesticide remain for hours or days to kill or must it touch the insect when applied?
IPM (Integrated Pest Management) guidelines call for assessing the damage any insect has done or is doing before you take drastic measures to destroy or control it. Unless you know the identity of an insect and know it is too destructive for you to tolerate, it’s a good idea to just let it go, for most insects are beneficial.
Send garden questions to firstname.lastname@example.org or Gardening, The Statesman, P.O. Box 40, Boise, ID 83707.