Insects as Helpers

Insect Friends of Man

F. C. Bishopp.

We must spend some time in our gardens watching insects at work to appreciate how they cooperate in giving us food, flowers, and comfort and to know that insects are not all bad.

Some insects improve soil. Air penetrates the soil through the burrows of ants, grubs, beetles, and wild bees.

These burrowing hordes also bring earth to the surface from the deeper soil layers and thus aid in improving its physical condition and in burying decaying vegetable matter. The grubs, or larvae, of many wood-inhabiting beetles, ants, termites, and minute insects (like the springtails) are constantly at work, tearing to pieces leaves, twigs, and trunks of fallen trees so that they may be returned to the soil to provide nutrients for other plant growth.

Insects hasten the decay of animal bodies and their return to the soil. Thus they figure in the endless cycle that involves all life. Not that the insects engaged in soil-forming activities are wholly beneficial. Some, like white grubs and cicadas, in their young stages may damage plants by feeding on the roots and (as adults) by attacking the stems, twigs, leaves, or fruit. Others, such as blow fly maggots, after they have done their work of carrion disposal and soil penetration may become disease-bearing flies.

Some other helpful insects we call predators and parasites.

The predators are the lions and tigers of the insect world. Some devour a large part or all of their prey. Others, such as the ant-lions, merely suck the body fluids.

The predatory insects of greatest economic importance are the dragonflies, damselflies, aphis-lions, ground beetles, lady beetles, and syrphid flies. Among the many other predators are the ant-lions or doodle-bugs, robber flies, snipe flies, tiger beetles, and wasps and ants.

DRAGONFLIES AND DAMSELFLIES are interesting and familiar. There are about 2,000 known species, 300 of which occur in the United States. The gauzy-winged, brilliantly colored creatures called dragonflies, devil's-darning-needles, or mosquito hawks live around ponds, lakes, and swamps. Their enormous eyes, made up of as many as 20,000 sight units, or facets, occupy a large part of the head and are so curved as to permit the insect to see in all directions at once. A network of veins covers the two pairs of large, rigidly extended wings.

Its highly developed eyes and speedy flight enable the dragonfly to catch in flight the mosquitoes and other small insects that are its only food. In flight the legs form a sort of basket into which the small insects are scooped. The dragonfly, while still on the wing, promptly devours the insects with its stout jaws, which work sidewise. Among our dragonflies is the big green darner, Anax Junius.

The dragonflies are fast fliers and may travel far. Some of the larger species commonly hunt several miles from their breeding grounds. They migrate long distances when swamps dry up. Migrations from Australia to Tasmania, 200 miles away, have been recorded.

The damselflies are smaller and more delicate than the dragonflies, flit about more leisurely, and fold the wings on the back when at rest. They prey on small, soft-bodied insects.

The young of dragonflies and damselflies, known as nymphs or naiads, destroy mosquitoes and other insects in the water. These strange-looking creatures live among the debris of stones on the bottom of streams and ponds. They have an odd, jointed extension of the under lip, or labium, which folds over the mouth parts but can be suddenly extended to grasp prey with its two powerful hooks.

The tiny naiads usually grow to full size, 1 to 2 inches long, in several months, but some species may spend 3 or 4 years in this stage. When it is grown, the naiad crawls out of the water on a stick or stone. When it has dried off, the skin splits down the back, and the head, thorax, netted wings, legs, and finally the long abdomen are drawn out. Soon the beautiful wings are spread, the metallic colors appear, and the new predatory life begins.

Enallagma exsulans, a damselfly.

THE APHIS-LIONS are among the most helpful insects of prey. There are 15 families in this group of nerve-winged insects. All are predaceous. Among them are the dobsonflies; the ant-lions, or doodle-bugs; and the aphis-lions, or golden-eyed lacewings.

The aphis-lions are in gardens everywhere. They destroy many kinds of destructive insects, the eggs of many caterpillars, all stages of plant-feeding mites, scale insects, aphids, and mealy-bugs.

Aphis-lions are the young, or larvae, of delicate, gauzy-winged insects with rather long antennae and beautiful golden eyes. These lacewings often are seen crawling about on the leaves or flying rather clumsily from plant to plant. The many species have similar habits and general appearance. Some are pale green. Others are brownish. The adult lacewing usually lives 4 to 6 weeks. In that time the female may lay several hundred eggs.

To keep the ravenous little aphis-lion that first hatches from devouring its brothers and sisters before they hatch ( and perhaps to give protection from other enemies), the mother lacewing lays each oval egg on the top of a delicate stalk projecting from the surface of a leaf or twig. The incubation period is 6 to 14 days. The larvae are odd, grayish-brownish creatures. They have a rather broad abdomen and conspicuous curved jaws, which extend forward from the head. With its pincerlike jaws the larva seizes its prey and sucks out its body juices.

When the larvae attain full growth, in 2 or 3 weeks, they spin oval, yellowish-white pea-sized cocoons on a leaf. The larva in its spinning operations tops off each cocoon with a circular cap, which the pupa pushes off when it is ready to become an adult. The change to the adult stage takes 1 to 3 weeks in warm weather.

PRAYING MANTIDS are odd-looking relatives of the grasshoppers. The name comes from the attitude they assume as they rest on twigs or stalk their prey.

The Chinese mantis is 4 inches long and can capture, hold, and devour large insects. Since it came into the United States about 1896, it has spread through much of the East. Like all members of its family, it lives on insects in its nymphal and adult stages. The mantid is cannibalistic. The female devours the male with which she mates and often eats her own young.

The eggs, laid in rather large masses, are firmly attached to twigs of trees. Each mass contains 50 to 400 eggs. A female often deposits 3 to 6 masses. Winter is passed in the egg stage. There is usually only one generation a year. The young resemble the adults except that they have no wings.

LADY BEETLES have habits that are anything but ladylike. Both the young and adult beetles kill and greedily eat various soft-bodied insects. Most familiar are the bright reddish-yellow species, which has black spots on the wing covers, or elytra, and the black species, which has red spots. Less well known are the numerous minute black species. Not many persons associate the rather clumsy-looking dark-colored larvae with the bright-colored adults. Neither do gardeners, familiar with the Mexican bean beetle and the squash beetle and their depredations, recognize them as lady beetles gone astray. Many of the lady beetles are native to the United States. Their combined action in destroying the eggs and young of destructive aphids, scales, and other soft-bodied plant-feeding insects is of great value to those who raise crops and flowers.

Sometimes they are called lady birds, as in the old rhyme : "Lady bird, lady bird! Fly away home! Your house is on fire, your children do roam."

The eggs of lady beetles are oval and Yellow or orange. They are laid in small masses, usually on the under side of leaves, and hatch in a few days. The Young larva, with its six long legs and tubercle-covered body, starts in search for soft insects. It devours one aphid after another. In about 20 days it becomes full-grown and is about one-fourth inch long. It then attaches itself to a leaf or stem by the tip of its abdomen, draws itself up, and pupates. The cast skin often remains more or less over the pupa. The adult splits the pupal skin and crawls forth to make further inroads on the fast-multiplying aphids. Some species congregate in great masses in the fall and spend the winter in that way in some protected place.

The vedalia, the small, reddish-brown Australian lady beetle, has done yeoman service against the cottony-cushion scale on fruit trees in the United States, Hawaii, New Zealand, and other countries into which it was imported to do just that.