302 INSECTS AND MAN 



During the course of this indoor work an unlooked-for 

 difficulty arose. The larvae of the brown-tail moth are 

 exceedingly hairy, their hairs are freely shed and are 

 irritating and poisonous. The atmosphere of the laboratory 

 in which the work was carried on soon became charged 

 with them, they penetrated the skin, noses, and throats of 

 the laboratory assistants, many of whom became ill and 

 resigned their posts. Gloves, masks, and even head-pieces 

 were designed to mitigate the evil, but with only partial 

 success, and eventually Mr Titus, who had been in charge 

 of the work, was obliged to resign in order to save his life, 

 for intense irritation of the lungs had been set up by the 

 hairs. 



Shortly after this misfortune, a move was made to 

 larger central laboratories at Melrose Highlands, and an 

 European depot was established at Rennes, in France. At 

 the French depot insects from Eastern Europe, destined 

 for America, were examined, repacked, and taken by hand 

 to Cherbourg and Havre for shipment; permission was 

 also given for the landing of all such packages without 

 customs examination, in short, everything possible was 

 done to expedite transit. 



Why, it may be asked, have the Americans gone to such 

 trouble and expense to introduce several parasites to assist 

 in the control of these two moths, when a single species of 

 ladybird was capable of rendering a destructive scale insect 

 innocuous ? A study of insect parasitism is necessary before 

 the question can be adequately answered, but, in brief, it 

 may be stated that parasitism plays varied r61es in the 

 economy of different hosts. Some insects support an 

 abundant parasitic fauna, while others are attacked only 

 by a few and perhaps relatively uncommon parasites. 

 Probably no two hosts, unless they be practically identical 

 in habit and life-history, are attacked by quite the same 

 species of parasites. There are, however, certain features 

 in the parasitism of each species which are common to 



