Does herd formation reduce insect harassment among reindeer? A field experiment with animal traps

This description of experiments in Finland on the hypothesis that herd formation in reindeer (Rangifer tarandus) can reduce harassment by insects was presented at the Third International Reindeer/Caribou Symposium, held at Saariselka in August 1982. Simulated animal traps, baited with carbon dioxide and using dichlorvos to kill the flies taken, were laid out as if to represent single animals or a dense herd of 24 animals. Simuliids and ceratopogonids were the most frequent Diptera taken, together with some tabanids. The number of flies caught was clearly dependent on the position of the ’animal’ in the ’herd’, and traps in the outer ring of the array appeared to be less frequently visited by insects than single traps. These results support the hypothesis tested.