Flight activity of the blowflies, Calliphora vomitoria and Lucilia sericata, in the dark.

Many species of insects are able to fly at night or in very low light intensities. The question of whether calliphorid blowflies are also able to do this to locate a corpse and oviposit nocturnally is of considerable forensic importance. However, to date studies of this behaviour have been contradictory. Here, the activity and number of Calliphora vomitoria L. and Lucilia sericata (Meigen) (Diptera: Calliphoridae) caught on sticky-traps were examined in a slow-speed wind tunnel, at different intensities of artificial light. The traps were either unbaited or baited-with liver. The number of both species caught, decreased incrementally as light intensity was reduced. While the responses of the two species were broadly similar, L. sericata were significantly more active than C. vomitoria, especially at higher light intensities. The number of flies of both species that were caught was higher in the presence of liver bait, but the presence of the liver bait did not change the shape of the relationship between catch and light intensity. Hence, light intensity acts as an independent exogenous stimulus for activity and although liver volatiles increase activity levels, they are not necessary as an activation stimulus. Comparison of the numbers caught in small or large enclosures suggests that any flies caught in darkness probably alighted on the trap by chance and that in darkness, while flies may be activated by carrion odours, they do not appear to be able to navigate effectively to the source of that odour. The results presented here suggest that in darkness, the probability of oriented flight leading to oviposition on a corpse by either species, is relatively low.