DAMAGE by slugs in gardens and farms is usually worst in late autumn and early spring. There are three reasons for this. First, some species are most numerous in winter1. Secondly, alternative foods are scarce, and crop plants such as germinating wheat or the young shoots from delphiniums are sometimes almost the only food available. Thirdly, slugs are active at temperatures which would put most cold-blooded animals into chill-coma.