Strategies to avoid biting flies by reindeer: field experiments with silhouette traps.

The effects of differences in grouping patterns (clumping vs. solitary) and habitat (open vs. forest) of reindeer (Rangifer tarandus) on attack rates by blood-sucking flies (Simulium truncatum, S. rostratum, Eusimulium pusillum [S. pusillum], Culicoides pulicaris, Haematopota pluvialis, Chrysops relictus and Hybomitra spp.) were studied using CO2-baited "reindeer-like" silhouette traps in Finnish Lapland near the Arctic Circle during June-August 1982. Within the grouped traps (24 traps per group) in an open habitat, flies attacked peripheral traps more frequently than middle and central ones. In an open habitat, flies preferred isolated to grouped traps. Isolated traps placed in the forest were attacked by flies less frequently than grouped ones in an adjacent open area. The results suggest that the gregarious females and calves of open country reindeer are less subject to insect attack than the more solitary males, and that forest reindeer may use the forest as a refuge from insects.