How to obtain it. 



21 I 



hide, and this they do under stones, or water plants, or anything 

 that comes handy, and they feed chiefly at night. 



The most favourable places for them to thrive and increase 

 seem to be shady, overgrown, shallow streams, where they are 

 seldom disturbed, and in such places they multiply very rapid y 

 indeed. I have met with them, too, in reservoirs and lakes,. 

 where they also seem to thrive ; and in open brooks they usually 

 find plenty of shelter amongst submerged marginal plants or their 

 roots, or under stones, etc. Aquatic birds generally know where 

 to find them, and should not be allowed to enter any places where 

 gammari are cultivated. In open streams and lakes it does not 

 matter so much, as they can there take care of themselves. It is 

 most suggestive of shrimps to see the way in which a v/ater hen, 

 for instance, goes poking about in their hiding places among the 

 marginal grasses, or the stones at the head of a shallow. Decaying 

 animal and vegetable matter constitutes the food of this crustacean, 

 and it seems to thrive equally well in cold spring water or in that 

 of a higher temperature, though it usually attains a rather larger 

 size in water that warms up well in the summer. 



Fig. 28. Dyt scits uiarginalis and larva. 



There are a great many aquatic beetles, but they do not 

 possess a very high food value. They are hard cased and exceed- 

 ingly voracious, and probably destroy far more food than they 

 yield, so there is no economy in encouraging their presence. The 

 two largest are Dytiscus marginalis and Hydrophilus piceus. The 

 former is carnivorous and very fierce, and will attack and kill fish 

 up to the size of minnows, both in its larval and perfect form. As 

 a beetle it is well known, being a conspicuous object, but in its 



