( cxxxv ) 



possess an automatic apparatus for equalising bodily temper- 

 ature, so that it only varies by a few degrees, whatever the 

 external conditions, but an insect must rapidly acquire the 

 temperature of its surroundings. The ordinary returns of 

 temperature as published give us only that of the shade, and 

 therefore fall short of indicating the heat which objects attain. 

 For example, the average amount of sunshine in France has 

 recently been stated to be about 30 per cent, more than in 

 England, and therefore its crops and its insects must get much 

 more heat than the difference of the mean temperatures in the 

 two countries indicates. But sunshine may mean much more 

 than this to the many insects whose activity is confined to the 

 periods of sunshine, the difference between the temperature of 

 objects " in the sun " and those "in the shade " being enormous, 

 often 20°-30° F. (say IT-IG" C), equal, while it lasts, to the 

 difference between the mean shade temperatures of England in 

 January and in July. Moreover it is quite conceivable that heat, 

 intermittent and at the same time intense, especially when 

 associated, as it often is, with dryness, may suit many insects 

 much better than equable heat, though the average degree of 

 the two may be nearly the same. The direct heat from the 

 sun is especially great in mountain regions * and others where 

 the air is very dry, and its effect on insects is increased by their 

 habit of basking, especially if on a heat-reflecting surface. 

 This habit is frequent with larvas, so that some species cannot 

 be reared without exposure to sunshine ; and many butterflies 

 will not pair or lay eggs in the shade. 



In some countries the excessive abundance of insect life is 

 doubtless to be accounted for by the shortness of the summer 

 season. This is the case in many of the higher elevations in 

 mountain regions, where only a very few hot months separate 

 the spring snows from those of autumn. 



Temperature has obviously much to do with geographical 



insects ; the perception of a bright light, as we know, has an effect of 

 marvellous power on many. Cclcena haworthii is an example of a species 

 that flies by day in warni overcast weather, not on a clear sunny afternoon. — 

 Tutt's " Hints," vol. i, p. 89. 



* See Hann's " Handbook of Climatology," translated by Ward, chap. xii. 

 Dr. Hunter Workman, addressing the Royal Geographical Society, 

 21st November, 1904, referring to altitudes of from 21,500 to 23,394 feet 

 in the Himalayas, speaks of the intense h.eat at noon. 



