344 BOARD OF AGRICULTURE. [Pub. Doc. 



fatally poisoned. Other instances which were brought to 

 light where poultry was destroyed by a small quantity of 

 Paris green indicated that birds were peculiarly susceptible 

 to arsenical poisoning. 



Since wholesale spraying for the gypsy and brown-tail 

 moths began, in 1905, the finding of dead birds and the dis- 

 appearance of living birds have been frequently reported. 

 The arsenate of lead used in spraying for the gypsy moth 

 is necessarily applied in much greater strength than the 

 Paris green formerly used. Paris green can hardly be ap- 

 plied at a strength of 1 pound to 150 gallons of water without 

 danger of destroying the leaves, and so defeating the purpose 

 of spraying; but the arsenate of lead, properly made, can be 

 sprayed with success at five to ten times this streng-th without 

 injuring the foliage. In some cases this poison is used at 

 such strength as to injure horses or cows grazing beneath 

 the trees. 



Arsenical insecticides do not kill insects by contact. The 

 foliage is covered with the spray, so that leaf-eating insects 

 may consume the poison with the leaves; they are thus poi- 

 soned internally. AVhen it was seen that most of the gypsy 

 caterpillars were uninjured by Paris green at the maximum 

 strength at which it could be safely used on foliage, chemical 

 tests were made of the internal organs and tissues of cater- 

 pillars that had fed upon it. A living and apparently healthy 

 caterpillar was found to contain (in proportion to its size) 

 twelve times the dose of arsenic which would be fatal to a 

 normal man. Such caterpillars evidently eliminated the 

 poison and lived. Some that had died apparently of arsen- 

 ical poisoning had eliminated practically all poison from the 

 system before succumbing to its effects.^ Birds will not eat 

 sickly or dying insects when they can procure healthy ones, 

 and the habit of rejecting sickly larvae had been supposed to 

 render birds safe from arsenical ])oisoning from such sources. 

 But if caterpillars in apparent health are able to carry much 

 larger doses of arsenic in proportion to their size than would 

 kill a man, the danger to birds, susceptible as they are to 



1 Forbush, E. H., and Fernald, C. H., "The gypsy moth," Massachusetts State Board 

 of Agriculture, 1896, pp. 475, 476. 



