We investigated male clustering behaviour in large bulk cultures of th
e American house dust mite, Dermatophagoides farinae. Aggregation in t
he colony was restricted to males only. The water loss rates for indiv
idual males in isolation and as a group of six were determined. Males
in a group of six retained water nearly twice as effectively (they had
lower rates of net water loss) than individuals. Clustering is thus a
n adaptive behaviour to help reduce water loss. Because the clustering
response was observed exclusively by males, this behaviour may serve
an additional purpose system that involves a pheromone system. (C) 199
8 Chapman & Hall Ltd.