Blow fly artifacts from blood and putrefaction fluid on various surfaces: a source for forensic STR typing

Abstract

Adult blow flies can deposit small spots ('artifacts') containing biological fluids like blood on various surfaces at a crime scene, either by regurgitation or defecation, and thereby create new or modify existing stains. These minute traces may represent evidence for the past presence of a certain person or victim in crime scene scenarios where nobody is present or all other crime-related biological traces have been cleaned up. We analyzed artifacts on crime scene relevant surfaces (glass, wood, concrete, wallpaper, carpet, plastic wrap), produced by the forensically important blow fly Calliphora vicina Robineau-Desvoidy (Diptera: Calliphoridae) after ingesting fresh and degraded porcine blood as well as putrefaction fluid from a pig's trotter and evaluated the potential of these spots for short tandem repeat (STR) analysis at various time intervals after deposition. Genotyping was possible on single fly artifacts on all surfaces up to 300 days after deposition by the flies after both blood or putrefaction fluid intake. The results indicate that the suitability for STR typing of those spots mainly depends on the time since deposition. The activity of flies at a crime scene can lead to artifacts which areeven 300 days after depositiona valuable source of case-related DNA. Sometimes those traces may even be the only source of information for DNA profiling.

Location of Artifacts Deposited by the Blow Fly Lucilia cuprina After Feeding on Human Blood at Simulated Indoor Crime Scenes

“…Under many conditions, artifacts may be found in low areas in large number. The results, when considered in the context of previous research , also demonstrated that flies may indeed move human DNA from one location to another, particularly in climatic conditions during which they are most active. The spread of artifacts throughout the house confirms that flies will often move some distance (in these experiments, their movement was restricted to a maximum of 16 m) after feeding before defecating or regurgitating.…”

Crime scene and body alterations caused by arthropods: implications in death investigation

“…Among these, 7 were case reports [13][14][15][16][17][18][19], 3 case series [6,20,21], 19 original articles [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40], 4 were technical notes [41][42][43][44] and 8 were reviews [1,10,[45][46][47][48][49][50].…”

Distinction of Fly Artifacts from Human Blood using Immunodetection

“…terraenovae , following blood feeding, four types of artifacts (regurgitate, defecatory, translocation, and transfer patterns) are produced that met the definition of insect stain, yet none can be distinguished morphologically from human bloodstains in a consistent or reliable manner . These limitations have been reported for at least 6 other species of cyclorrhaphous Diptera ; Adult necrophagous flies can produce artifacts as a result of feeding on several types of fluids other than human blood (e.g., saliva, semen, vaginal fluids, and decomposition fluids), which yield artifacts that vary widely in terms of shape, color, and size, that vary based on the surface in which they are deposited, and that are indistinguishable from human body fluids based on appearance ; Contextual analysis does not overcome the limitations of visual analysis, especially when the insect stains lack tails and are intermixed with human body fluid stains, and/or the artifacts are of similar size to body fluid stains ; The artifacts of only 6 species from two families (Calliphoridae and Sarcophagidae) of necrophagous flies have been examined in any detail, and all are primarily laboratory‐based observations . Thus, it is difficult to come to any consensus on the typical classification of fly artifacts or accurate methods of detection of insect stains found at crime scenes. …”