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There is a tendency to regard all insect life in the garden as potentially harmful to plants, but not all insects are bad news - some are real allies in the fight against pests. It's important to be able to recognize who your friends are, because most insecticides are not so discriminating, and spraying and killing any natural predators will make the problem worse.
Beetles
Although some beetles are pests, there are many useful species. These include ground beetles, which live on the soil surface, hunting out insects, slugs, and worms during the hours of darkness; rove beetles such as the scorpion-like devil's coach horse; and the familiar ladybugs.
Capsids
Yes, some capsids are well-known pests but there are other species which are definitely helpful to gardeners. The best known is the predatory black-kneed capsid that helps control aphids and red spider mites on fruit trees. Similar in appearance to capsids are anthocorid bugs, another useful ally, especially on fruit.
Centipedes
Golden brown centipedes scurry over the soil in search of prey - insects, their eggs and larvae, along with small slugs and worms. They are often confused with millipedes (a pest) but millipedes are darker, have more legs that form a thick fringe down the sides, and roll up into a ball rather than running for cover when disturbed.
Hoverflies
Hoverflies could easily be mistaken for bees at first glance, though their method of flight is quite different - they hover almost stationary in the air, then make short, sharp darts forward. When they are at rest it's evident that they only have one pair of wings, unlike bees and wasps that have two. The larvae of the various species of hoverfly are very small, but most are efficient predators of aphids and other soft-bodied insect pests.
Lacewings
Lacewings are very delicate insects with pale green, almost translucent bodies, large, lacy wings and very long, constantly moving antennae. Both the adult lacewings and their larvae eat aphids; the larvae are rather insignificant, long-bodied creatures that are pale brown. Lacewings are found all round the garden, and are often attracted by lighting into houses at night.
Ladybugs
Nearly everyone can recognize ladybugs, but perhaps not so many could identify their larvae. While the adults are almost universally regarded as harmless, their small, armadillo-like, blue and orange larvae are likely to be treated with more suspicion, and are often destroyed "to be on the safe side."
Both adults and, more particularly, larvae feed on large numbers of insect pests, especially aphids. A single larva can consume up to 500 aphids in its three-week life. Before emerging as an adult ladybug, the larva pupates, and the yellow pupa may be mistaken for a Colorado beetle, which it superficially resembles. Ladybugs are most commonly red with either two or seven black spots, but they may also be black with red spots, yellow with black spots and black with yellow spots.
Wasps
Wasps, as everyone knows, sting, and at the end of the summer they are a real nuisance, feasting on ripe fruit, and ruining picnics and outdoor meals. Leaving aside this antisocial behavior, for the rest of the year they are a definite asset to gardeners because they collect all manner of soft-bodied grubs and insects to feed to the young wasp larvae in the nest. Other, less highly visible wasps are also extremely useful - several species are parasitic, laying eggs in the bodies of insect pests that hatch out and slowly consume their hosts. Ichneumon wasps are some of the best known, though rarely recognized in the garden. They have long, slender bodies and are not brightly colored like the common wasp.
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