Exclusion of forensically important flies by the red imported fire ant (Solenopsis invicta) in southeastern Texas

On 3 March 2009, the remains of a middle-aged white male were partially buried at the Southeastern Texas Applied Forensic Science (STAFS) Center at Center for Biological Field Studies (CBSF) at Sam Houston State University. The individual was buried to expose a post-mortem abdominal wound intended to attract carrion flies. Worker ants of a colony of Solenopsis invicta (Buren) (red imported fire ant) immediately filled in the wound with soil thereby monopolizing the exposed area of the corpse and excluding expected carrion insects from the wound. At no time, until abdominal eruption, were adult flies able to oviposit on or near the wound and no maggots were observed. After eruption, approximately one week post-burial, the ants were sufficiently disturbed such that flies were able to oviposit and maggots were able to colonize the corpse. At this point, the anticipated insect succession for this biogeoclimatic area proceeded. Estimation of the post-mortem interval based on the minimum period of insect activity would be severely skewed should the remains be discovered at this point and maggot growth rate be used as the primary determinant for the PMI. While S. invicta is an expected member of a carrion ecosystem in southeastern Texas and is known to distort the PMI estimation through maggot and egg removal, the complete exclusion of flies from the wound by S. invicta burial behavior was unexpected and as far as we are able to determine an unpublished occurrence.