The forensically important blow fly, Chrysomya megacephala (Diptera: Calliphoridae), is more likely to walk than fly to carrion at low light levels.

One factor that influences estimates of time since death using entomological evidence is whether or not blow flies nocturnally oviposit. Field studies focusing on egg laying have found it occurs on an inconsistent basis. A key but poorly understood factor in nocturnal oviposition is a blow fly's ability to locate carrion under low light levels. It has been speculated that blow flies are more likely to walk than fly to carrion during the night, but this has not been empirically tested. We directly compared guided walking versus flying using infrared sensors under low light levels in laboratory conditions for Chrysomya megacephala (F.) (Diptera: Calliphoridae), a blow fly previously described to be nocturnal. We found C. megacephala is more likely to walk than fly toward carrion under low light levels (p=0.016). We did not, however, find differences between males and females for walking (p=0.48) or flying (p=0.42) despite male C. megacephala possessing eyes better suited for increased light capture. These results demonstrate the need to better understand where blow flies go at night, as bodies found within a fly's walking distance are more likely to be colonized.