How to obtain it. 209 
The red ones (Arachnida histrionica) look particularly bright 
and attractive, and trout fry will often turn and follow them, but, 
for some unexplained reason, they do not seem to eat them. It 
is well known that some spiders are poisonous, and this may have 
something to do with the matter. Livingstone Stone says :—‘“ If 
a trout not over two-and-a-half inches long strikes at a black 
spider in the water, the spider will strike back at him, and if he 
takes a good aim will kill the trout instantaneously. The little 
fellow will not go twelve inches before he turns over on his back, 
and drops down dead.” ‘This is what happens in America. 
It is a pleasure to turn from the mites to the water boatmen. 
Entomologists speak of the large ones as Wotonecta glauca. They 
are about three-quarters of an inch Jong, by about hardly a quarter 
wide, and have two long ciliated oars to swim with, from which 
they derive their name. The largest yearling trout devour them 
greedily. The smaller ones fight for them, but the fry stand a 
poor chance—they being the prey of the beetles, who mercilessly 
harpoon them. Fortunately, although a common insect, they do 
not usually abound in great numbers in trout waters. They 
delight in the stagnant, or semi-stagnant, waters of ponds and 
ditches, in both the larval and the mature stages. Here, again, is 
a wonderful provision of nature for the production of a large food 
supply for the trout, when they have grown somewhat. The 
insects may be cultivated in special ponds, and swept out with a 
suitable net as required. 
Another genus, the Covixzde, containing some thirty species, 
must have our attention. Of these Corixa vulgaris is perhaps the 
commonest. In general form it very much resembles a /Vo‘onecta, 
but it swims the other way up ; that is, with the oars underneath, 
and it is only about a quarter of an inch long. Some members 
of the genus attain a length of half an inch. They are very 
pugnacious, and are carnivorous in their habits, eating decaying 
animal matter, and attacking any living creature that is not strong 
enough to resist them. They swim by means of rapid strokes of 
their oars, which gives them a jerky movement. They are air 
breathers, coming to the top of the water for an instant every few 
minutes. When the fry are two months old, or even before if 
vigorous, they hunt corixa like a pack of hounds, and eat them 
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