236 ARTIFICES OF ANIMALS. 



offspring; When that operation is performed, they leave the 

 coasts and disperse in the ocean, till the same instinctive 

 impulse forces them to observe similar conduct the next sea- 

 son. This migration of salmons, herrings, and many other 

 fishes, from the ocean to the rivers or shores, is of infinite ad- 

 vantage to mankind. It is upon their passage that such 

 immense numbers are taken to be used as food, and thus be- 

 come an important article of commerce. 



The insect tribes, though comparatively diminutive, are not 

 deficient in artifice and address. With much art the spider 

 spins his web. It serves him the double purpose of a habita- 

 tion, and of a machine for catching his food. With incredi- 

 ble patience and perseverance he lies in the centre of his 

 web for days, and sometimes for weeks, before an ill-fated fly 

 happens to be entangled. One species of spider, which is 

 small, of a blackish color, and frequents cottages or out-houses, 

 I have known to live, during the whole winter months, almost 

 without the possibility of receiving -any nourishment ; for, 

 during that period, not a fly of any kind could be discovered 

 in the apartment. If they had been in a torpid state, like 

 some other animals, the wonder of their surviving the want 

 of food so long would not have been so great. But in the 

 severest weather, and through the whole course of the winter, 

 they were perfectly active and lively. Neither did they seem 

 to be in the least emaciated. 



The formica-leo, or ant-lion, is a small insect, somewhat 

 resembling a wood-louse, but larger. Its head is flat, arid 

 armed with two fine movable crotchets, or pincers. It has 

 six legs, and its body, which terminates in a point, is composed 

 of a number of membranous rings. In the sand or in finely- 

 pulverized earth, this animal digs a hole in the form of a 

 funnel, at the bottom of which it lies in ambush for its prey. 

 As it always walks backward, it cannot pursue any insect. 

 To supply this defect, it lays a snare for them, and especially 

 for the ant, which is its favorite food. It generally lies con- 

 cealed under the sand in the bottom of its funnel or trap, and 

 seldom exhibits more than the top of its head. In digging a 

 funnel, the formica-leo begins with tracing a circular furrow 

 in the sand, the circumference of which determines the size 

 of the funnel, which is often an inch deep. After the first 

 furrow is made, the animal traces a second, which is always 

 concentric with the first. It throws out the sand, as with a 

 shovel, from the successive furrows or circles, by means of 

 its square, flat head, and one of its fore legs. It proceeds in 



