The first army of snails arrives in early spring. It attacks the tender shoots and devours our favorite seedlings. Gardeners put out pellets of poison and still more snails are eaten by the birds. Their numbers decrease   but the war is not won. A few weeks later, a new snail army crawls into the garden and this goes on all summer.

Each army of snails hatches from broods of tiny eggs left to hatch on the ground by their parents   who are usually members of the previous army. The eggs and baby snails escape notice because they are so tiny. But a snail rarely strays more than a few yards from his cradle   which means that the grown snails in your garden have lived there for many generations. Most of them perish after a few weeks or months, though a few live to be two years old.