Dr. Murai Éva - Gubányi András szerk.: Parasitologia Hungarica 27. (Budapest, 1994)

been isolated and identified. The method was described in detail earlier (Halmai 1978, 1984). At the beginning of the 1980's an unusual finding was the presence of some little legs in the bodies of several D farinae females. At first I did not pay attention to it, thinking that they were particles of the larva developing in the body of the female, which incident was not an exceptional one. However, later they were found in the body of young forms and males as well and similar particles of other mite species could also be seen in the house-dust mites. Since then more attention has been paid to this incident, even by systematic reinvestigation of the previous material. It turned out to be a remarkably common phenomenon. The preliminary results were reported earlier (Halmai 1986). RESULTS Chitinous particles of legs and chelicera of other Dermatophagoides mites were regularly found in the bodies of D farinae, mostly in females. Some specimens contained only one leg, some others were almost full of mite pieces. Their presence was rather conspicuous in some females besides an egg containing developing larva. However, not only D farinae females showed this phenomenon, but sometimes males and nymphs, rearly D. pteronyssinus and exceptionally D. chelidonis and a tyroglyphid female as well. Most chitinous particles seemed to be preserved. In some rare cases pieces could be observed inside a faecal pellet. Occasionally some particles of the predator cheyletid mite was also observed in D. farinae females (See Figs 1-2). DISCUSSION The phenomenon "cannibalism" is not always clearly understood. Cheyletus eruditus females either eat their own larvae because they have a restricted "hunting field", guarding the eggs for a long time, or they control the population because of shortage of food. D. farinae and D. pteronyssinus mites were supposed to act like cannibals in the upper layer of their culture, because there "other mites were the only source of food" (Brody et al. 1972). In any case their extremly strong chelicera enable them to crush very hard particles (Griffiths and Cunnington 1971, Bronswijk 1973). What can be the reason for such behaviour of house-dust mites in their natural habitat? Is that a sign of thanatochresis (Perez and Atyeo 1984), i.e. the use of chitinous particles of other dead mites for the production of egg-shells for example? In this case the digestion would presumably be more active, more effective, and we could not identify these structures in the faecal pellets of mites. However, this does not exclude the utilization of their juicy part. Could the chitinous material be perhaps used for the production of new cuticle during the process of molting? In this case mostly the nymphs should behave in this manner and not the females. Moreover if it were a natural way of their development or feeding mechanism, then it would be an everday incident. However, Spieksma (1986, personal communication) did not observe this phenomenon during his several-decade extensive investigations of house-dust mites. This phenomenon was observed in our series collaterally with the increasing incidence of D. farinae, both in absolute and relative terms. More mite particles occurred when the density was high, when the rate of young forms in their population