Enemies 7 



Blood-worms are preyed upon by many aquatic insects, Enemies, 

 as well as by fishes. Caddis- worms, Perla-larvae, Sialis- 

 larvae, and Tanypus-larvae devour tlieni greedily. A 

 number of empty heads of the blood-worm may often be 

 seen in the stomach of a single Perla or Tanypus larva. 



If it is desired to get a supply of blood-worms, a slow, Method of 



, . . , . collecting. 



muddy stream, abounding m decaying organic matter, 

 should be visited. Pure water is not at all necessary to 

 the health of the larvae, and they often abound in foul 

 streams. A long-handled iron spoon or ladle, which can 

 be tied to a walking-stick if necessary, is a convenient 

 collecting implement. The larvae may be picked or 

 Avashed out of the mud, and brought home in a wide- 

 mouthed collecting bottle. They can be kept alive for 

 weeks with very little attention. Decaying vegetation 

 and fresh water now and then are all that they require. 

 A shallow vessel is better than a deep one for these and 

 most other aquatic insects. 



In winter captive larvae continue a long time without Transfer. 



. -, , mations. 



marked change. Young ones grow bigger, and now and 

 then moult, though it is rare that we see anything of the 

 operation. A cast skin enables us to make out that the 

 dorsal wall of the thorax splits along the middle line, 

 while the head breaks up along two sutures which define 

 the central plate (clypeus), and also along the mid- ventral 

 line. When the larvae are nearly an inch long, they will 

 often remain for many weeks together without visible 

 alteration. But in summer, in a particularly warm 

 winter- season, or in a well-warmed room, matters advance 

 more rapidly. If we see larvae with the rings behind 

 the head swollen, we know that they will shortly turn to 

 pupae. When the last larval skin is cast, there emerges 

 a very difi'erent-looking animal, in which we can make 

 out with a little pains a pair of wings, six long legs, and 

 a head with big, compound eyes. These organs belong 



