38 INSECTS AND MAN 



yellow, black-spotted larva lives within the branches of 

 many species of trees, and, in doing so, destroys them. The 

 goat moth, Cossus ligniperda, is an even worse offender in 

 this direction. Its larva, when full-grown, attains a length 

 of ten centimetres, is reddish-brown above and creamy- 

 yellow below, and has an evil "goaty" smell. As these 

 larvae live within the trees, willows for the most part, for 

 three years and feed all the time, the amount of damage 

 they do may be easily imagined. Other destructive, wood- 

 boring Lepidoptera are, the currant clearwing, Sesia 

 tipuliformis, and the apple clearwing, Sesia myopiformis, 

 damaging currant bushes and apple trees respectively. 



LOCUSTS 



The majority of people, unscientific people that is, when 

 questioned as to the most destructive economic insect, would 

 assuredly reply, the locust. The reply might not be 

 absolutely correct, but it would show that the locust is, 

 by tradition, one might say, fixed in men's minds as an 

 injurious insect. One of the plagues of Egypt took the 

 form of a swarm of locusts, and, from that day to this, 

 these insects have been the cause of very considerable 

 financial loss to mankind. What is a locust ? The name 

 is loosely applied : in some countries grasshoppers are called 

 locusts ; elsewhere, locusts become grasshoppers ; and again, 

 at times, insects of other orders are named locust, apparently 

 for the sole reason that they appear in swarms the periodi- 

 cal cicada is a case in point. Strictly speaking, the locusts 

 comprise about six species of the Acridiidce, a family of the 

 Orthoptera. 



We will not attempt to describe the various species 

 of locust, but will devote a few words to the habits of 

 these insects in South Africa, where they have done more 

 damage and hindered agricultural progress to a greater 

 extent than anywhere else in the world. In our intro- 



