Pesticides are chemicals designed to kill invertebrates, usually insects, which have become plant pests. Farmers and gardeners have been spraying their crops and flowers for years to protect them. Although effective they can have a disastrous effect on a habitat’s food web. As well as the insect pests, useful invertebrates may also be killed. The small birds may eat the poisoned invertebrates and take a certain amount of poison into their own bodies. They may not be killed outright, but the poison may weaken them and their eggs may be infertile. At the top of the chain, the sparrowhawk may eat many poisoned birds and be affected in turn. In the 1960s, numbers of birds of prey in Britain began to decline drastically because of the use of pesticides called organochlorines. Fortunately, these pesticides were banned from use some years ago and since then populations of birds of prey have begun to recover.
Chemicals upset the balance of life in a habitat and a gardener who cares for wildlife does not use them. Even if you grow vegetables in your garden, the pest which attack these can be kept fairly well under control by the many predators you have encouraged into the garden habitats. For example, slugs and snails are eaten by hedgehogs and song thrushes. If slimy molluscs are eating their way through your lettuces, it is very tempting to go out and buy a packet of slug pellets – but if a hedgehog or thrush eats dozens of poisoned slugs and snails, the poison builds up and kills them. There are all sorts of “green” ways to deal with unwanted pests, which do not affect the food chains. Organically grown vegetables are much safer for humans too!
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