Some of Nature's Methods of Subduing Injurious Insects. 181 



of the caterpillars they attack, placing them in small groups, on the back a 

 short distance behind the head, where they are firmly glued to the surface. 

 The young larvte when hatched pierce through the skin of the caterpillar 

 and feed upon its substance in a manner similar to that of the ichneumon 

 parasite. 



Caterpillars are also subject to the attacks of contagious diseases, which 

 sometimes carry them ofi' by thousands. Those reared in confinement, such 

 as silk-worms, are often decimated by these plagues, and those species which 

 swarm on our trees and vines, and also in our fields, are also affected in a 

 similar manner. These diseases are generally held to be of fungoid origin, 

 and are communicated either by contact or by spores disseminated in tlie 

 air. Large numbers of the forest tent caterpillar (C. isiocampa sylvatica) are 

 often destroyed by this means. The larvae are usually almost full grown he- 

 fore they are attacked ; then, when the disease reaches a certain stage, they 

 remain motionless, fully extended and retaining a firm hold on the trunks 

 of trees, on fences, or any other material on which they have been crawling, 

 and shortly, although they retain for a time a natural appearance, they 

 will be fovmd to be quite dead, and their bodies so softened as to burst with 

 a very gentle handling. A species of QAii-v^orm, Agrotis fennica, which has- 

 been very abundant and quite destructive to clover and other crops in some 

 parts of Canada and in Michigan during the past year, has been so badly af- 

 fected by the same disease that it has been difficult to rear any of them tO' 

 perfection. Out of some fifty or sixty specimens collected by me for this 

 purpose, nearly all were affected by this disease, and only one lived long 

 enough to become a chrysalis, and this one did not mature the perfect insect. 

 Even winged insects are not exempt from such diseases. The common 

 house-fly is very subject to a fungoid disease in the autumn, the spores and 

 filaments of which multiply with amazing rapidity in the fluids contained in 

 the fly's body, and soon destroy life, forming a circle of luxurient growth all 

 around the body of the victim. Examples of this may be found on the win- 

 dows of almost every dwelling during the months of September and October. 



The last agent we will mention as sometimes fatal to insect life, is a sudden 

 frost. It is well known that the eggs of insects will remain uninjured 

 through our most severe winters, but after hatching, if soon exposed to the 

 depressing influences of frost, the young caterpillars die in great numbers. 



Thus we see how parasitic enemies, fungoid diseases and climatic changes 

 are so many controlling agents, used by a wise Creator to keep in check the 

 undue increase of such insects, which by their wonderful fecundity would 

 without them bid defiance to all man's efforts at repression, and cause the 

 horticulturist to lament with the ancient prophet, "That which the palmer- 

 worm hath left hath the locust eaten, and that which the locust hath left hath 

 the canker-worm eaten, and that which the canker-worm hath left hath the 

 caterpillar eaten." 



