THE SOIL FAUNA: ANTHROPODS - The Soil - page 93

As hunter-gatherers, pastoralists, horticulturalists and artisans, the reputation and in-
fluence of ants in soil communities is unique. One cannot but be impressed by the
sense of energy, organization and purpose centred on a large nest of the wood-ant
Formica rufa in a pine wood. Several species of ants have colonies of 10,000 or more
individuals but F. rufa colonies are reputed to reach 300,000. Many invertebrates are
taken as prey by some species of ants, but a motley retinue of mites, insects and oth-
er arthropods are scavengers and commensals within ant's nests. The most famous
of these dependants, of course, is the large blue butterfly. Its larvae are taken under-
ground by ants, and live in the nests for nine months feeding on the ant brood and pro-
ducing attractive secretions in return. They can only produce these secretions in their
last larval stage, and so they remain very small until they have been adopted and then
grow enormously in the nests of their host ( Fig. 32 ) .The main requirements of this
rare and handsome insect have been known for some time - its need for wild thyme
plants for egg laying in addition to the ant colonies for larval development. Unfortu-
nately, the extent to which the large blue larvae depended on a particular species of
ant, Myrmica sabuleti , was not fully realized; nor that this ant depended on extremely
closely grazed turf, less than three cm high. By the time research had unravelled the
complex details it proved too late to halt the spiral of decline that led to the extinction
of the large blue in Britain in 1979. The story shows just how subtle can be the inter-
connections between soils, soil animals, plants, flying insects and grazing mammals.