Ants and Habitat Specificity in Aphids

A number of rare butterflies are known to only utilise their host plant species when they grow in particular situations. Field data are presented showing that two rare species of aphid also only utilised their host plants when they grew in particular situations, namely near ant nests. The oak-feeding aphid Stomaphis quercus only occupied trees within 17 m of a Lasius fulignosus nest. The thyme-feeding aphid Aphis serpylli only occurred in a region of a Breckland grass heath where the sward contained a high density of Lasius niger nests, and then most commonly only in quadrats containing ant nests. The sward that was suitable for A. serpylli was generated by the action of farm traffic. It is concluded that ants indirectly impose habitat specificity on these aphids.