FIELD BOOK OF PONDS AND STREAMS 



submerged water plants ; these later break up into short pieces 

 from a fraction of an inch to an inch long. 



Although the life histories of many hairworms are unknown, 

 those of certain species have been studied and the main facts 

 discovered. In Gorditis rohtistus, the egg hatches into a 

 minute larva which goes swimming about in the open water 

 and after a time drops to the bottom and bores its way into 

 any animal which it can reach. Hundreds of these young 

 hairworms squirm over the pond bottom, most of them are 

 probably lost, yet many of them manage to get inside the 

 bodies of aquatic insects. A few of them wriggle out of the 

 water and onto the wet soil of the shore, and are there eaten 

 by grasshoppers which come to the water's edge in search of 

 food. Occasionally they are eaten by crickets; both kinds of 

 insects take animal as well as vegetable food. Within a grass- 

 hopper the hairworm grows, finally reaching maturity. 

 When thus fullgrown its problem is to reach the water again 

 and if the grasshopper frequents the water's edge at this 

 time, the fullgrown hairworm will burrow out of its body. 

 Whether it is influenced by the moisture is not known but this 

 seems probable. Once in the water the hairworms mate and 

 lay eggs that hatch into larvae which begin the cycle all over 

 again. Obviously but few hairworms which enter the bodies 

 of grasshoppers ever get back to the water. Most of them 

 must perish because the grasshoppers are not about the water 

 at the right time or more often fail to go near it at all. Yet 

 this and other species of hairworms produce so many eggs 

 that the race is kept going in spite of the great mortality 

 which befalls its members. 



Two common hairworms. — Two of the most widely dis- 

 tributed hairworms are Paragordius varius and Gordius villoti 

 first called G. aquaticus by Montgomery; these are common 

 through most of the United States (Fig. no). Males of 

 P. varius are nearly 14 inches long, over 2 inches longer and 

 more slender than the female, the hind end of the body is bi- 



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