244 THE CANADIAN ENTOMOLOGIST 



in heat and light, dressed in white in the winter, on the principle that, as he was 

 a warm-blooded animal, this costume would reduce to a minimum the radiation 

 of heat from his body. Conversely, the snow- flea being a cold-blooded animal, 

 with no bodily heat to lose, finds its dark pigmentation advantageous in assist- 

 ing it to absorb heat when it comes to the surface in winter. 



A great many species of Collembola survive the northern winter, but 

 the snow- frequenting habit is sharply confined to certain kinds, while other 

 closely allied species never emerge while the snow is on the ground. Available 

 North American and European records credit about one- half of all the snow 

 appearance, accidental or intentional, to the genus Isotoma. The other genera 

 represented are Entomobrya, Achorutes, Onychiurus, Anurophorus, Orchesella, 

 Tomocerus and Sminthurus. My experience in this district also is that Isotoma 

 can claim more species on the snow than any other genus, Isotoma nigra 

 MacG. is the most abundant of the genus here, and it is sometimes found over 

 many acres of open woodland or beaver meadow, with a frequency of one or 

 two specimens to the square yard. /. palustris Mull., more local in its distri- 

 bution, often reaches about the same frequency in swampy places. /. mac- 

 namarai Fols., which affects wet places also, is scarcer, and it usually takes 

 some searching to collect a dozen or so specimens. /. viridis Bourl. var. riparia 

 Nic. I have found only towards spring. Once I collected 25 or 30 specimens in 

 April on the snow covering a rather dry pasture, but mostly they are found 

 sparingly in woods. A couple of other Isotomas of undetermined species are 

 represented by only a specimen or two, and the appearance of one at least was 

 accidental. Also a few odd specimens of Tomocerus sp., Orchesella sp. and 

 Entomobrya sp. had evidently not come out of their own accord where I found 

 them. Among the real snow travellers, however, we must class Achorutes 

 armatus Nic. It never emerges in very large numbers, but I have found it 

 active on the snow in the vicinity of small streams from November to March. 



Very seldom do any of the species mentioned so far ever appear on the 

 snow in sufficient numbers to attract the attention of the casual wayfarer; no 

 one but the entomologist who is looking for them is likely to notice them. This 

 does not mean, however, that the insects occur only sparingly, for many people 

 are extraordinarily insensible to phenomena that do not affect them directly, 

 and even when in large numbers, snow- fleas are often passed by unnoticed. 

 One morning, crouched on my snowshoes in a narrow pathway through a cedar 

 swamp, I was picking up Isotomas with a small brush and dropping them into 

 a vial, when I heard another snowshoer come crunching over the crust towards 

 me. It was a labouring man of my acquaintance with his axe on his shoulder, 

 taking a short cut to his work across, the Ottawa River. He gave me a polite 

 "good-day," but looked so curiously at my occupation, that in order to preserve 

 at least the remnant of a reputation for sanity, I thought it well to explain 

 to him what I was doing. He was greatly surprised to see the insects on the 

 snow. They were plentiful that morning, and for some distance he had been 

 crushing scores of them under his snowshoes at every step, but he had not 

 noticed them until I pointed them out to him. "Well, by gosh!" he said, "I 

 often heard tell of snow-fleas, but I never seen them before." A worthy man 

 as I know, though imperfectly instructed in sframmar. 



