COLEOPTEKOUS INSECTS. 95 



The Lampyridce, issuing in myriads from their re- 

 treats, diffuse their mild effulgence over the plants 

 and shrubs, which they often cover with their num- 

 bers ; and the luminous Elateridce dart about in all 

 directions, filling the air with their radiant tracks. 

 This natural illumination does not cease till the ap- 

 proach of day. 



Although these insects, as has been stated, gene- 

 rally increase in number as we proceed from the 

 poles to the equator, yet there are some exceptions 

 to this rule. Among these are the aquatic beetles 

 (Dytiscidce), which are most numerous in the tem- 

 perate zone, and also of larger size than within the 

 tropics. At the same time there is scarcely any 

 tribe of Coleoptera more widely distributed than 

 this ; a circumstance no doubt attributable to the 

 equable temperature of the medium in which they 

 live, which exempts them in a great degree from 

 the modifying influence of climate. Of this a fami- 

 liar proof is afforded by our native Colymbetes, which 

 continue pretty active throughout the winter, when 

 other insects are in a state of torpidity. We have 

 occasionally seen them swimming with alacrity in 

 the waters of a pond when the surface was covered 

 with a thick coating of ice. The same circumstance 

 that accounts for their extensive diffusion, may there- 

 fore be regarded as the cause of their not increas- 

 ing in tropical regions. In the latter countries, be- 

 sides, every pool or stagnant water, such as these 

 creatures love to frequent, is dried up during one 



