Before a hurricane great flock of birds will be seen roosting. This New England saying has much truth in it, for an animal grazes with its tail to the wind. In as much as an east wind is a rain wind and a west wind is a fair wind, the grazing animal's tail becomes a weather sign. If corn husks are thicker than usual, a cold winter is ahead. The higher the clouds, the better the weather.
Higher clouds indicate both dryness of air and higher atmospheric pressure.
Both these qualities are present with fair weather. There seems to be no reason for this to be true, although many people still use it as a weather sign. This rule does not always apply, but insects do calling more during moist weather, as flying is more difficult. Heat causes human sweating, which makes you a more appetizing target. Theses two reasons, plus a release of more body odors when atmospheric pressure on your body lowers, will add up to the rule that flies and insects are more bothersome just before a rain than at any other time.