In order to assess the effect of alternating electromagnetic and direct magnetic field on adult Helix aspersa O. F. Müller and their eggs, adults and eggs of H. aspersa maxima Taylor and H. aspersa aspersa O. F. Müller were exposed to such fields with different parameters, and the following life cycle traits were observed: condition of hibernating adults, their survival rate during hibernation and reproduction, egg mass, hatching success, growth rate of hatchlings and body mass of next

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... n adults. Adults were exposed to sinusoidal, alternating electromagnetic fields of 50 Hz, 100 Hz and 200 µT, and magnetic induction of 50 Hz, as well as a field of 175 µT and 10-1000 Hz (repetition period 80 minutes). Egg batches were exposed to direct magnetic fields of magnetic induction 5 µT and 10 µT and alternating electromagnetic fields of analogous induction and frequency of 50 Hz. The effects varied depending on the parameters of the fields, subspecies and life cycle stage. Adult H. aspersa maxima was more sensitive to the changes in characteristics of electromagnetic field than H. aspersa aspersa, but the two subspecies showed a similar reaction to exposing their eggs to direct or alternating magnetic field. Probably direct field had a greater selection effect compared to alternating field, removing weaker genotypes at embryonic stage; this resulted in a greater mean body mass of the next generation adults. The results are preliminary; further studies, with further modifications of parameters of the fields applied are necessary.