Dr. Kassai Tibor szerk.: Parasitologia Hungarica 2. (Budapest, 1969)
ta"blished by BALOGH (1953). The communication of the several species usually occurs between neighbouring horizons only. Rare exceptions naturally occur, e.g. a squirrel flea ( M.s .sciuro rum ) found on one occasion on a fox; it might have arrived on its unusual host either by having fallen from the nest or in the course of the food-chain, or eventually from the ground, as, for instance, was the squirrel flea collected by soil surface extraction methods. On the basis of my experiences gained in the course of collections and investigations, I venture to state that a great majo rity of flea species appear to be more bound to certain types of nests and their microclimate than to the hosts themselves . I shall try to prove this assertion by some examples. The fox and the badger inhabit the same biotope where in most of our mouse species also occur, but I have never found a flea species parasitizing mice on either the fox or the badger. Similarly, the characteristic fleas of these latter two hosts have never occurred on mice ,although there are innumerable opportunities for the exchange or transmission of fleas living on these hosts. That is not to say, however, that one or two mouse fleas will not be found on fox or badger, or vice versa, though this can only be an occasional phenomenon. (Even in the literature there are only a few records of such an occurrence.) In my opinion, lack of such interchange of flea species is not due simply to differences in the hosts, but to the fact that nests of mice have a completely different microclimate from those of the deep subterranean burrows of the fox and the badger. Incidentally, PETJS (1953) has already pointed out the importance of the correlation between the occurrence of certain flea species and the environmental factors, so my experiences would seem to corroborate his statements. A certain kind of correlation in the systematical relationship of the hosts and their fleas (and also their other parasites) appears to be frequently demonstrable.This statement apparently contradicts my previous assertion, because it might be supposed
