COLEOPTEEOTJS INSECTS. 
95 
The Lampyrid&y 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 
