Do sandy patches help reindeer against insects?

Sandy patches such as river banks, roadsides and sand pits are the preferred resting places for populations of reindeer and caribou during the insect season. In northern Finland, they are used mainly in July-August, when tabanids are on the wing. The occurrence of blood-sucking insects on a grassy meadow and on a sandy river bank was studied in July 1981 with the aid of Manitoba traps baited with carbon dioxide. The daily mean catch of tabanids and (in brackets) simuliids was 26 (589) on the meadow and 5 (179) on the sandy bank. The daily available flying time (temperature above 15°C) was nearly the same at the 2 sites, but the maximum temperatures were considerabale higher on the sandy bank than on the meadow. It is suggested that, on the sandy bank, carbon dioxide released from the trap rises with the heated air, with the result that insects find the trap less efficiently than on the meadow.