Almost nothing is known about the natural ecology of the nematode Caenorhabditis elegans, including its interactions with parasites. To help rectify this discrepancy, we assessed natural variation in the response of C. elegans towards a potential parasite, the soil bacterium Bacillus thuringiensis. Our results show that 10 isolates from across the world differ significantly in survival rate and infection level when confronted with a parasitic strain of B. thuringiensis. Furthermore, behavioural responses are identified as an important component of C. elegans defence, including evasion and possibly reduced ingestion of parasites. Again, the natural isolates show significant differences in these traits. In conclusion, worm defence is indicated to be complex and variable across space, implying that parasites play an important role in the ecology of this species. Based on these results, we expect C. elegans to be a promising model host for future analysis of the evolutionary dynamics of parasite-host interactions.