FIELD BOOK OF PONDS AND STREAMS 



spring from it before they are landed. When handled they 

 give off a milky fluid with a peculiar odor. In aquaria the 

 males often make squeaking noises b}'' rubbing the under- 

 sides of the wing-covers against the body. 



There are two common genera of Gyrinidce, Gyrinus in- 

 cluding the smaller whirligigs (Fig. 210) and Dineutes, the 

 larger whirligigs (Fig. 211). 



Adults of Dineutes which are kept in captivity will devour 

 with avidity any freshly killed larvae. Wilson fed these to 

 whirligigs which he was observing and writes, "As many as 

 could would seize the insect, crowd around it, grasping it, 

 whirling around it in wild curves and sometimes diving be- 

 neath the surface, but always holding on to their prey and 

 tearing out mouthful s of insect tissues." 



Their oval white eggs are laid on the under surfaces of 

 lily pads (Fig. 18), or on Potamogeton leaves. Each egg is 

 glued separately to the surface of the leaf. 



Larvae of whirligigs. — The larvae of some insects, such as 

 caddis worms, are very familiar, while adults are almost un- 

 known, but this situation may be quite reversed. Thus among 

 the whirligigs the adults are often seen, but the larvae almost 

 never. They are pale, slender creatures which crawl over the 

 bottom trash or swim through the water with a sinuous motion 

 of their bodies which is aided by eight heavily fringed gills 

 which hang from each side of the abdomen. They are adepts 

 at clambering backwards or forwards. On the tip of the 

 abdomen there are four sickle-shaped hooks which they catch 

 into anything convenient and pull themselves backward 

 after the manner of caddis worms. 



Whirligig larvae capture young mayflies and dragonflies but 

 they are less rapacious than some of their reb.tives. They 

 can be kept in aquaria and will thrive on nymphs of the may- 

 fly, CallihcEtis (p. 208). In Gyrinus larvae (about one half 

 inch long) the first two pairs of gills are fringed like the others, 

 in the larger Dineutes (one inch) these two pairs are with- 



272 



