The washing away of wrongs: Validation of the bloody scythe and fly

The Washing Away of Wrongs is an ancient Chinese manuscript for forensic medical examiners that contains the first recorded use of entomological evidence to solve a murder.  During an official inquisition, the murderer confessed when he saw flies attracted to the blade he had used and no other blade despite his effort to wipe his blade clean.  To validate this story, trials comparing insect attraction between a bloody knife (wiped clean and dry) and wet knife (wiped dry) were conducted in 30 different rural locations throughout the Pineywoods ecoregion of Texas.  Twenty-eight of the 30 bloody knives were contacted by insects with an average time to first contact at 1.8 minutes.  Both the number of interactions by different individual insects and the total number of contacts by all insects was significantly greater for the bloody knife than the clean knife, which indicates that insects can detect and will interact more frequently with tools that have traces of blood.  Insects that came into contact with the clean knife did not linger and instead passed over it to either reach the bloody knife or leave the study area.  Surprisingly, Calliphoridae flies were only present in 3 trials, with either Sarcophagidae or Formicidae dominating most trials.  This study explores quantitatively the ubiquity of insects and their attraction to traces of Suidae blood during warm temperatures in this ecoregion.  These results add data to the length of time expected before insects first contact a food resource.