How to obtain it. 



221 



frequently, but whether they actually remove anything from the 

 fish, or simply anchor themselves, and there feed on very minute 

 animalcula>, we could never be quite sure ; but this much is certain, 

 they do not leave behind them a scar of any sort that we could see. 

 The members of the leech tribe (Hirudinea) are all more or 

 less dangerous to fish. They leave scars which soon form 

 suitable resting places for the spores of Saprolegnia, and this 

 often proves fatal. The great flat-footed leech ( Geometra piscicola) 



Fig. 44. Geoinetra piscicola (en'arged). 



and its cousin, the horse leech ( Aulostomum gulo) are both 

 unwelcome visitors in fish ponds. The horse leech is very 

 common in many waters, and is well known, and when it attacks, 

 fish, the loss of blood from its tri-radiate bite is very weakening. 

 It is true that the trout will eat the leeches, but we much 

 prefer keeping them out of the places where trout are, as they 

 destroy more than they produce as food. In their youth, their 

 principal food consists of the larvae of flies and small insects. 

 They seem particularly fond of caddis worms and soon unhouse 

 and eat them indeed they seem almost designed by Nature to 

 be the bete noir of these creatures. All the leeches are free swim- 

 mers, progressing by an undulatory vertical movement. They also 

 crawl fast, and are capable of living for some time out of water, 

 so they are not very easy to get rid of. Fortunately they are not 

 very prolific ; about twenty eggs per annum seems to be their rate 

 of increase. 



Most anglers will have met at some time or other with a 

 beautiful greenish crab-like creature adhering to fish, which is 

 commonly called a "tick." They vary in size from one to three- 



