ii6 THE FOOD OF ANIMALS 



mouth-parts are in a very much reduced condition, and jaws 

 may be altogether absent. The aquatic larvae, on the other 

 hand, have a relatively long term of existence. They differ 

 largely in character in different species, and it is only the flattened 

 forms that are exclusively carnivorous. Stone-Flies {Perlidcs) 

 (see vol. i, p. 375) form a related group of insects in which the 

 mouth-parts of the adult are feeble but the aquatic larvae are 

 carnivorous. 



The Caddis- Flies [Phryganeidcs) (see vol. i, p. 375) are 

 insects of moth-like appearance, and in the adult state are not 

 predaceous. The aquatic larvae, known as " caddis - worms ", 

 build cases for themselves from various materials, and as they 

 are mainly vegetarians would not be mentioned here were 

 it not for the peculiar and interesting habits of one group 

 {Hydropsychidce), in which the larvae are carnivorous, at least 

 in certain cases. They live in fixed dwellings made of sand or 

 little pieces of stone fastened together with silk, and with this 

 same material they construct snares in which small aquatic 

 creatures are entangled. An account has been given of a 

 Brazilian species in which the larvae are found in the rapid parts 

 of small streams, the houses of a number of these, as many as 

 thirty, being placed side by side in a transverse row on top of 

 a stone; there being also in some cases several parallel rows of 

 them. The mouth of each habitation faces up-stream, and ex- 

 pands into a large funnel-shaped "verandah", over which a 

 net of silk is spun. A North American species proceeds in a 

 somewhat different manner, for it spins a wide-meshed net across 

 the stems of water-plants, &c., in the neighbourhood of its 

 dwelling, where it lies in wait for any prey that may chance to 

 be snared. There is another allied group {Rkyacophilides), in 

 which also the larvae inhabit fixed cases, and one case is described 

 where the front-legs are provided with strong forceps, evidently 

 used for seizing prey. 



STRAIGHT-WINGED INSECTS (Orthoptera) 



These are insects with typical biting mouth - parts, which 

 have been described in the case of the Cockroach (p. 102). The 

 large majority of the species feed upon vegetable matter, or at 

 most on a mixed diet, but a striking exception to this is afforded 

 by the Soothsayers or Praying Insects {Mantidce\. These are 



