The relationship between Insects and Man is one of wariness a strange situation. There are as many benefits to be gained from insects as there are discomforts. It is conventional to classify insects as helpful or harmful when discussing their relationships with men. But it is often forgotten that the majority of insects have no obvious connection with man at all.
This is not to say that there is no link of any kind. In ecological kind terms, nothing lives alone, and if you follow insect food chains you find some interesting. If there is a tenuous connection linked with our own activities. Take dragonflies hawking up and down a stream, they keep well out of our way but serve us well by keeping down the mosquito population.
On the other hand, the dragonfly is one of the hosts of a parasitic flatworm affecting chickens and their egg production. This is a case where one insect species is both good and bad. However, there are many other insects that all have much stronger and more tangible human connections.
Bees and Other Allies
The honey bee is at or near the top of every list of useful insects, qualifying on several counts. The honey amounting to some five and a half million pounds a year, is obviously very important and so is the beeswax we use for making polishes-but these materials are really far less vital than the bee’s role in pollinating our flowers and crops.
In their relentless search for nectar and pollen, the bees ensure that flowers are pollinated and have a chance of setting seeds. Bee stings can be dangerous to a few people who are especially sensitive badly. Although fatalities are rare-but there is also evidence that the venom is useful in them reacting to treating rheumatic conditions.
Green lacewings (along with ladybirds) are another group of man’s allies because of the war they wage against greenflies and other aphids. You can use them for small-scale biological control in the garden by collecting the adults and larvae and putting them on aphid-infested plants. But large-scale rearing of lacewings for this purpose does not seem feasible.
An entire army of scavengers is employed in clearing up the dead bodies and the excrement of other animals, making the countryside more attractive as well as releasing nutrients for reuse by the plant community. They are not driven by an innate desire to tidy up the land, of course. The corpses and excrement are food for these insects and young.
The burying or sexton beetles are well-known for their disposal of small corpses. Working in pairs, they bury the corpse by digging soil from underneath it. The female lays her eggs on or near the corpse so that the young have a food supply of flesh and maggots.
Both on the farm and in the garden crop pests are among the most familiar harmful insects. The damage done by the caterpillars of the large white butterfly is all too familiar to the gardener, and anyone who raises brassicas from seed will also know the infamous flea beetles, which chew small neat holes in the seedling leaves. Leather jackets do equally serious damage below ground.
Aphids, generally known as black flies and greenflies, are sap-sucking bugs that play havoc with many crops. The mechanical damage is caused by thousands of tiny needle-like proboscis projecting into the plants and withdrawing sap.
That causes much distortion of growth, but even more serious are the numerous virus diseases (sugar beet yellow, and potato mosaic, for instance) carried by the aphids. Insect larvae occur in many fruit crops, notably raspberries and apples. Several attack apples, but the most familiar is the grub of the codlin moth, a small pink caterpillar.
Trouble in the Store
Our problems with insects do not stop when the crops have been harvested. Many pests continue to eat the produce in the store, and they are joined by many specialists-the stored product pests. On a global scale, it has been estimated that about one-quarter of the world’s food supplies are destroyed at, or after, harvest by pests.
Most damage occurs in tropical areas, but many of the tropical insects have found conditions in our granaries and flour mills to their liking and established themselves here long ago. The grain weevil is one of the most serious grain destroyers.
Both adults and larvae feed on grain, and with each female laying up to 200 eggs it is easy to see why infestations build up so easily. The Mediterranean flour moth is another serious pest, causing losses in flour mills.
All parts of the trees are attacked by various kinds of insects. One of the worst offenders is the bordered white moth whose larvae, known as pine loopers, strip the needles from large areas of plantation pine trees. The insect that has caused the most dramatic impact on our countryside in recent years, however, is the elm bark beetle carrier of the Dutch elm disease.
Pests in the House
The most serious household pests are the timber feeders that attack the very fabric of the house. Several species of beetles are involved here, with the common woodworm being the most abundant. The woodworm is, of course, the larva which tunnels unseen through rafters, floorboards, and furniture.
The adult, a small brown bullet-shaped beetle, is commonly known as the furniture beetle. It has been estimated that some 75% of buildings harbor this pest which, when present in large numbers, can reduce sound timber to dust within a few years.
Carpets, clothes, and other fabrics suffer from the attention of numerous pests, including carpet beetles, fur beetles, and clothes moths. As far as clothes moths are concerned, it is the larvae that do the damage. They are among the few lepidopterous larvae that feed on animal material-hair, wool, and feathers. (Their natural homes are the nests of birds and rodents, where they find plenty of natural fibers.)
Biters of Man
The insects that attack our own bodies are the most unpleasant of all the pests, and the most abundant are the various kinds of flies. Mosquitoes are well-known blood-suckers, the females generally needing a meal of blood before they can lay their eggs.
Anti-coagulants are injected into the wound while the insect feeds, and these can cause symptoms ranging from mild irritation to severe blistering. Mosquitoes capable of carrying disease still exist here and could cause problems if malaria ever returned.
Potentially less serious, but even more of a nuisance, are the millions of tiny midges that tickle and bite us, especially in upland areas. Other biters-more correctly described as pierces and suckers-are the horseflies and insidious clegs.
The latter fly silently and land on us unnoticed until the sharp beak goes in for a meal. Even the houseman is not free from the biters, although modern hygiene has greatly reduced the number of fleas, lice, and bed bugs. The human flea is now rare, but cat and dog fleas can still be a problem in houses with pets. Typhus fever, dog tapeworms, and myxomatosis are all carried by fleas.
Our effect on Insects
Clearly, insects have had a great effect on man, but what of man’s effect on insects? Leaving aside the direct effect of the pesticides which we spray on them by the ton, the most important effect has been through changes to the insect’s environment, particularly the loss of habitats.
Modern hygiene has fortunately reduced the chances of coming across a bed bug in the house.
A bumblebee’s most important function is the pollinating of flowers-Darwin was able to prove that the amount of clover seed produced in a field depends on the strength of the bumblebee population. Unlike honey bees, their small annual colonies do not make a collection of their honey an economical proposition for us.
A 7-spot ladybird feeding on aphids and Ladybirds are allies of man because they prey on such pests. Their appetites can be immense, with a single large ladybird larva eating as many as 100 aphids in a day.
Not surprisingly, in some parts of the world, they are used for the biological control of pests. In North America, for instance, the Australian ladybird Rodolia cardinalia was introduced to control a pest-scale insect. Honey bees produce about 53 million jars of honey a year in the UK.
The housefly is unpopular since it deposits dangerous germs on food. The cockchafer and its larvae do great damage to plants.