LIFE HISTORY OF CHIRONOMIDS 475 



rest with the front legs elevated, though not all species have this 

 habit. In most Chironomidae the thorax of the adult insect 

 projects like a hood over the head, but in the subfamily Cera- 

 topogoninae, which alone interests us here, this is not the case, 

 and this negative characteristic is the best distinguishing mark 

 of the subfamily. 



There are a number of genera and many species included in 

 this group of blood-suckers, but they fall naturally into two groups 

 according to the habits and structure of the larvae. In one, of 

 which the principal genera are Ceratopogon and Forcipomyia, 

 the larvae differ from all other Chironomidae in being terrestrial, 

 living in damp places under bark, stones, moss, etc., and in being 

 covered with spines (Fig. 217). In the other group, of which the 

 principal genus is Culi- 

 coides, the larvae are 

 orthodox in being 

 aquatic and unspined 

 (Fig. 216C) ; a few spe- 

 cies are marine. Most 

 of the blood-sucking midges become active at dusk, but if dis- 

 turbed they will bite in the shade even on bright sunny days. 



Life History. The eggs of aquatic midges (Fig. 216B), sev- 

 eral hundred in number, are laid in water, either floating free or 

 moored to some object. Each one is covered with a gelatinous 

 envelope, and the eggs adhere in chains or in little masses, thus 

 resembling very diminutive bunches of frog or toad eggs. In 

 about six days, more in case of low temperature, the eggs hatch 

 into almost microscopic larvae (Fig. 216C). The latter are worm- 

 like creatures practically without hairs or spines in the aquatic 

 species, but with conspicuous bristles in the terrestrial forms. 

 Usually the only hairs present are in a pair of tufts on the last 

 segment. In most midge larvae there is a footlike outgrowth 

 on the first and last segments of the abdomen. The larvae have 

 inconspicuous blood-gills for breathing in water, and therefore 

 do not need air as do mosquito larvae. Most midge larvae are 

 free-swimming, but some excavate tubes in mud and line them 

 with a salivary secretion which hardens on contact with water. 

 The food consists of microscopic plant and animal life. The 

 pupa (Fig. 216D) rather resembles that of a mosquito, except 

 that the abdomen is kept extended instead of curled under and 



