Potential hazards of insecticides caused environmental pollution, insect resistance and disturbance of natural biological balance. The possibility of infecting the Acari, Argas persicus (tick bird) using two species of entomopathogenic nematode: Steinernema carpocapsae and Heterorhabditis bacteriophora was investigated. Different concentrations: 12000, 9000, 6000, 5000, 4000, 3000, 2000 & 1000 infective juvenile stages (IJS) of the two nematode species were used in the experiment. The study revealed that nymphs, male and females soft ticks were susceptible to the two used nematodes. The LD50 values were estimated for the two nematodes, respectively. Rates of mortalities differed according to host stage, the nematode species and concentrations of (IJS). It was of interest to mention that the nematodes could invade, kill the ticks but failed to reproduce inside the dead ticks. The influence of infected and non infected tick haemolymph on the development and migration of nematode inside cotton leaf worm, Spodoptera littoralis, the host choice of nematodes, was investigated. Mortality percentage with different values was observed after their injection with infected and non infected Argas haemolymph. Entomopathogenic nematode might be used as an alternative useful, safe and effective biological control agent in the future.