Abstract: 1. The average distance for fleas Neopsylla bidentatiforrnis and Citellophilustesquorurn sungaris to attack their hosts is less than 2 cm; the greatest distance does not exceed 10cm. Within effective attacking range, the number of blood suckingfleas is greater at short distance from their hosts than at long distance. 2. The frequency of host attack is higher in female fleas than in male, in sexually mature fleas than in newly emerged, in NeoFsylla bidentati/orrnis than in Citellophilus tesquorum sungaris, and on Mus musculus than on Citellus fauricus. 3.Within certain time after death of the host, a few fleas still （r） attack its corpse As the death time (x) prolonged the attacking fleas became fewer, and the relation may be expressed by the curve log logY=a- b·logX. 4. The time for fleas leaving from the host falls into a curve of partial distri bution which becomes more distinct when the temperature is higher. The rate for fleas leaving from the live host is as quick as from the dead host and it is almost identical for the two flea species. The average time for fleas to leave from theirhosts is negatively correlated to environmental temperature.

Key words: Neopsylla bidentatiforrnis——Citellophilus tesquorum sengaris host attack——leaving form host