32 NATURAL HISTORY OF AQUATIC INSECTS CH. 



early spring have passed the winter in a torpid 

 condition as full-grown Insects. A new generation 

 of larvae is now produced. They grow rapidly, pass 

 through their transformations, and emerge as perfect 

 Insects when the height of the summer is passed. 

 They are most plentiful about the beginning of 

 September ; after that, their numbers steadily de- 

 crease, and by the middle of November very few can 

 be found ; most of them have now retreated to their 

 winter quarters, though a spell of fine weather, even 

 in the depth of winter, will tempt a few to the surface. 

 They pass the winter months buried in mud among 

 the roots of water-plants, and can be dug out with a 

 scoop. If kept indoors in an aquarium, they clo not 

 become torpid, except in the severest weather. Under 

 such conditions their numbers rapidly decrease, for 

 food is scarce, and when the Insect is active, its 

 tissues waste. 



The full-grown Gyrinus, like most other adult 

 Beetles, flies with ease. It seems to be unable to take 

 flight from the surface of the water, but finds it 

 necessary first to climb up the stem of some water- 

 plant, where it rests for a time. Then it slowly opens 

 its wing-covers, extends its long wings, and takes to 

 flight. When kept in captivity, they are unwilling to 

 remain very long at a time upon the surface of the 

 water. They will climb up the glass sides of an 

 aquarium with great effort, making use chiefly of the 

 hindmost pair of legs, and struggling with the 

 tenacious film of water which they bring up with 

 them. 1 They will creep nearly an inch up the 

 1 The action is more fully explained on page 162. 



