The vertical movement of Turkish isolates of Steinernema feltiae (TUR-S3) and Heterorhabditis bacteriophora (TUR-H2) was compared at different temperatures in the presence and absence of larvae of the host insect, Galleria mellonella. Nematodes of both species moved faster towards the bottom of the column when an insect was placed there. Steinernema feltiae showed greater vertical dispersal ability than H. bacteriophora. The vertical movement of both species increased as the temperature increased and lower temperatures depressed the movement of H. bacteriophora more than S.feltiae. The nematodes that had migrated different distances were compared for their infectivity to G. mellonella and the positive correlations between distance travelled and infectivity indicate that there is a link between host searching behaviour and infection behaviour in S.feltiae and, to a lesser extent, also in H. bacteriophora.