Vol. LI. LONDON. DECEMBER, 1919. No. 12 



POPULAR AND PRACTICAL ENTOMOLOGY. 

 Further Remarks on Collembola. 

 by charles macnamara, arnvrior, ontario.* 



(Continued from page 245.) 



and more grateful air, come out in constantly increasing multitudes. 



Experiments showlfe^d that a temperature of zero Fahrenheit killed Achorutes 

 socialis in less than an hour, while at 5° F. they survived indefinitely. But 

 although 5° F. seems to do them no harm, they never expose themselves volun- 

 tarily to that degree of cold. The lowest temperature at which I have seen 

 them on the surface was 18° F., and that was very exceptional. As a rule they 

 do not appear until the thermometer approaches 25° F., and from 30° F. up- 

 wards they reach their greatest abundance. Their reaction to a rising tempera 

 ture is rapid. Even when the snow lies two feet deep or more, they are out 

 within an hour or so after the milder weather begins, and after 24 hours of thaw 

 they may be looked for in large numbers. No marked difference in response 

 to temperature changes can be noticed between the various snow frequenters, 

 and usually three or four different species can be found at the same time. In 

 this district Achorutes socialis is generally in excess of all the others, but oc 

 casionally, for some reason or another, the mild weather fails to attract it, 

 and Isotoma ni^ra or /. macnamarai may be the predominant species on the 

 snow. 



Outside of temperature, the other weather conditions have little influence 

 on them. Provided the day is mild, they come out as readily in wind, pouring 

 rain cr heavy snow as in calm sunshine. During a snow-storm it is interesting 

 to watch how they keep constantly climbing to the surface in order to avoid 

 being buried by the falling flakes. 



It is quite possible that sometimes the insects reach the surface by com- 

 ing up straight through the snow. Their integument is far too delicate for any 

 forceful burrowing, but snow lying loosely as it falls, always has interstices 

 between its particles amply wide enough for the free passage of these minute 

 creatures. This mode of emergence, however, cannot very often be used in 

 mid-winter, for generally the snow stratum, when it attains any thickness, 

 includes one or more layers of crust that are quite impervious to the soft-bodied 

 springtail. Nevertheless, another exit is open to them. Around every stalk 

 of grass, brushwood stem, tree trunk or other object projecting through the 

 snow, there is always a clear space, no matter how deep the snow, resulting 

 partly from the shrinkage of the snow as it settles, and partly from the radiation 

 of absorbed heat by the object. It is from these sally-ports that the snow- 

 flea hosts principally issue. 



* We regret the awkward division of Mr. Macnamara's article. Through an unfortunate 

 oversight the concluding sentence of the first part in the November number was left unfinished. 



26.5 



