The most common application of forensic entomology involves estimating a portion of the postmortem interval (PMI), which usually assumes that blow flies (Diptera: Calliphoridae) do not oviposit nocturnally. Research objectives were to (1) investigate blow fly nocturnal oviposition in relation to sunrise and sunset in Michigan; (2) evaluate abiotic variables postulated to affect blow fly oviposition; and (3) conduct laboratory experiments testing blow fly activity under complete darkness. In 2006, nocturnal oviposition was evaluated in relation to sunset by exposing pigs to fly colonization at 1-h intervals, beginning 2 h before and ending 2 h after sunset. This test was replicated in 2007; however, replicate pigs were placed in the field 2 h after sunset, and hourly observations were made into the following morning. Oviposition was never observed at night. In a laboratory experiment, Lucilia sericata (Meigen), never oviposited on liver hanging above or placed directly on the ground in a completely dark room, Another dark room laboratory study documented that adult flies launched into the air could not fly. This study documents that the probability of nocturnal oviposition on pig carcasses in Michigan was extremely low to nonexistent. These results should be considered when estimating a portion of the PMI in forensic entomological investigations.