338 On the Geographical Distribution of Insects. 



On the ai'rival of winter, no inconsiderable numbers still subsist, 

 concealed in their various retreats, but none are then disclosed, 

 except a few, such as Geometra brumaria, which darts about 

 our gardens even to the end of December ; Trichocera hyema- 

 lis, which may be seen during the fine days of winter perform- 

 ing their aerial dances above the snow ; Boreas hy emails, cer- 

 tain Poduria, and the Chionea araneoides, which are found 

 only on the snow itself. Winter, in our climates, thus divides 

 the year into two very distinct periods, and, by arresting ve- 

 getation, deprives insects of the means of existence. 



In the equinoctial regions, where winter is unknown, and 

 where the year is divided, more or less regularly, into two 

 seasons — ^the wet and the dry — without vegetation being ever 

 suspended, it might seem, at first view, that nearly an equal 

 quantity of insects should be found during the whole year ; 

 but this is very far from being the case. The seasons, in this 

 respect, are almost as determinate as in Europe. The dry 

 season has nearly the same efi^ect on insects that winter has 

 with us ; they disappear almost entirely, and are not again 

 visible till the rains. On the other hand, the latter, if they 

 reach a certain maximum, produce the same effect on them, 

 so that, m reality, their seasons of abundance are often rather 

 brief. This is the more obvious, the nearer we approach the 

 equator. 



Thus, in Guiana, the rainy season, which commences to- 

 wards the end of November, brings forth a considerable num- 

 ber of insects, which diminish rapidly in proportion as they 

 become more severe ; insomuch, that very few are to be seen 

 in January and February. In March, an intei*val of fine wea- 

 ther, which lasts for a month, and which the natives call the 

 March summer, causes them to appear in tolerable abundance. 

 From April to June, when the rains fall with such violence 

 that the country is literally inundated, the forests flooded and 

 shrouded in a cloud of vapour, insects completely disappear. 

 Towards the close of June, when the fine weather commences, 

 they again shew themselves, and increase with astonishing ra- 

 pidity till the end of August. This^ month, and that of July, 

 afford a richer harvest to the entomologist than all the rest 

 together. But the dry season, which is then confirmed, re- 



