The consequences of sheath loss on infectivity and behaviour of infective juveniles (IJ) were investigated in Heterorhabditis megidis. Ensheathed IJ were more infective, killing 32% of wax moth larvae, compared to 18% killed by exsheathed IJ. The percentage of time engaged in seven behavioural activities was recorded for individually stored IJ but no differences were found between exsheathed and ensheathed IJ. Immobility was the most common behavioural category exhibited by both exsheathed and ensheathed IJ, occupying one third of the observation time. Storage conditions affected the rate of exsheathment; 40% of IJ stored for 28 days in water in bulk (50 in 8 ml) exsheathed compared to only 23% of those stored individually (1 in 2 ml).