Although the tilt of the earth's axis is only a little over 23o, this is enough to provide the dramatic contrast between the heat of summer and the cold of winter as our planet rotates around the sun. These pronounced seasonal changes in temperature dictate the seasonal patterns that dominate the temporal patterns of life on earth. On a much shorter timescale, the daily rotation of the earth on its axis, yielding the day/night cycle, adds the important dimension of thermoperiodism that generates daily variation in the number of heat units that reach the earth's surface.

Certainly all animals are influenced by daily and seasonal cycles of temperature, but it is perhaps ectotherms, such as insects, that are most severely affected. With, at best, limited abilities to regulate their own body temperature, insects are at the mercy of the prevailing temperatures. Insects commonly use seasonal shortening in day length (photoperiod) as an environmental token to reliably signal the advent of inimical temperatures. For many insects these photoperiodic cues are used to program diapause, a period of developmental arrest used to wait out the winter months.