28 



RANDOM NOTES ON NATURAL HISTORY. 



Destroying Caterpillars. 



During the past year or two man}' inter- 

 esting experiments have been made and 

 valuable results obtained in the way of 

 artificial!}- introducing disease among com- 

 munities of caterpillars, a sort of caterpillar 

 plague or pestilence which carries them off 

 by thousands. There is a very fatal dis- 

 ease which appears from time to time 

 among silk worms, the larvoe of Bombyx 

 mori when bred for the production of silk, 

 a disease which spreads so rapidly that it 

 frequently destroys entire broods of cater- 

 pillars within a few days. So destructive 

 has it been that it is estimated that the silk 

 crop in Europe is damaged by it to the 

 extent of man}- millions of dollars annually. 

 During the past ten years it is believed to 

 have reduced the income of silk breeders 

 some twenty-five per cent., and in 1879 

 was said to be the main cause in the great 

 falling off in the silk crop of that year, which 

 was only about one-fourth of the amount 

 ordinarily produced. The celebrated Pas- 

 teur investigated this disease, and found it 

 to proceed from the presence of an exceed- 

 ingly minute form of bacteria, so exces- 

 sively small that it has been estimated that 

 it would require eight millions of them to 

 cover the head of an ordinar}' pin. When 

 water containing these minute organisms is 

 sprinkled on the leaves on which the silk 

 worms are fed, they are found to be rapidly 

 infected and capable of communicating this 

 pestilential disease to others with which 

 the}' are associated. The bacteria may be 

 preserved in a torpid condition without loss 

 of effectiveness for at least a year, probably 

 for several years, and that without any par- 

 ticular care, and when required for use can 

 be rapidl}' propagated in a suitable fluid. 



Throughout most of the State of Illinois 

 and in some parts of Michigan, it was 

 observed last autumn that a large proportion 

 of the cabbage worms sickened and died. 

 Hundreds of their bodies were to be seen 

 rotting on the cabbage leaves or shrunken 

 and dried to a blackened fragment. This 

 was soon brought under the notice of the 

 State Entomologist of Illinois, Prof. S. A. 

 Forbes, a most careful and indefatigable 

 observer, who at once proceeded to inves- 

 tigate the cause of this caterpillar plague. 

 He found the disease at first to be very 



unevenly distributed, some isolated fields 



showing no trace of it, while others not far 

 distant were fairly reeking with death and 

 decay, but as the season advanced it spread 

 in every direction until in some districts 

 almost every worm perished. He says, 

 "We can conceive something of the sig- 

 nificance of this disease if we imagine the 

 terror and dread which would seize man- 

 kind if such a plague should suddenl}' assail 

 human life. There would be no escape 

 for an}-, because the contagion would be 

 conveyed by the very food and drink b}- 

 which life was sustained." 



By dissecting specimens of the dead cat- 

 erpillars, the microscope showed their in- 

 testines to be full of undigested food and 

 swarming with a species of micrococcus, 

 which appeared in the form of excessively 

 minute spheres about one twenty-five thou- 

 sandth of an inch in diameter, sometimes 

 single, sometimes in pairs, and occasionally 

 in strings of from four to eight. He found 

 that these minute organisms could be read- 

 ily cultivated in beef broth, and that a 

 single drop of fluid from a diseased worm 

 introduced into a vessel of such broth, 

 w^ould in two or three days render the whole 

 contents milky with myriads upon myriads 

 of these microscopic organisms precisely the 

 same as those taken from the diseased 

 larvae. He also found by experiment that 

 the disease could be communicated to other 

 species of caterpillars. Experiments con- 

 tinued during the present year have shown 

 that by propagating this form of bacteria 

 in the manner described, and mixing a 

 pint of a well-charged culture with a barrel 

 of water and syringing cabbages with this 

 fluid, the disease may be introduced, thus 

 furnishing us with another means of defense 

 against some of these injurious insects. 



Wu. Saunders, Canadian Entomolof/ist. 



December, 1885. 



Mica in Canada. — During the past two 

 years muscovite has been discovered in Can- 

 ada in marketable sizes and paying quantity. 

 The Villeneuve Mine in the county of 

 Ottawa, has been worked continuously the 

 past year, and has produced many thou- 

 sands of pounds of mica, perfect in quality, 

 in sizes varying from sheets for stoves 

 up to plates 14x12 inches. — Canadiaii 

 Mining Review. 



