48 ZOOLOGY 



useful in furnishing food. Everyone knows how universally 

 shrimps are consumed, especially by the poor, and on the 

 coast of a small province like New Brunswick there are 

 800 institutions for "canning" lobsters. But the principal 

 importance to man of the Crustacea lies in the fact that 

 they form a great proportion of the food of fish, and the 

 shoals of fish whose erratic movements cause such distress 

 to fishermen are often determined in their wandering by the 

 presence or absence of swarms of Crustacea. In contrast with 

 the harmlessness of Crustacea lies the harmfulness of Insecta. 

 Amongst the few directly useful insects are the honey bee, 

 the silkworm, moth, and the cochineal insect. Honey is 

 food stored up in a cell made of an exudation of the insect's 

 skin called wax. Its primary use is the nourishment of the 

 developing young of the insect. Silk is a material secreted 

 by the grub or caterpillar of a moth, and is formed as threads 

 which are woven into a case or cocoon which shelters the 

 insect during a critical period in its growth. Cochineal is 

 a stuff contained in the bodies of the insects, and produced 

 by them from the juices of the plants on which they live. 



The only insects which may be said to be indirectly useful 

 are carnivorous insects, which destroy other insects, and such 

 insects as feed on the pollen and honey of flowers and thus 

 inadvertently carry pollen from one flower to another and so 

 effect the fertilisation of the egg-cell of the plant. This 

 fertilisation is necessary of course for the ripening of the fruit 

 and its contained seed. Insects are, in fact, man's great 

 competitors for the enjoyment of the fruits of the earth, 

 and when their numbers increase unduly man runs a great 

 risk of starving. Blood-sucking insects render life almost 

 intolerable in many regions of the tropics, and it has been 

 recently proved that, in addition to depleting the strength 

 of their victims by constant drafts on their blood, they 

 implant in them the germs of parasitic protozoa, which 

 run riot in their blood and cause fever and death. The 

 problem of the successful exploitation of the tropics, which 

 are the naturally richest regions of the earth, is largely a 

 problem of how to fight and conquer the insect life which 

 luxuriates there. It is little wonder that the study of insects 

 has acquired an importance which has raised It to the rank 



