Morphological characterization using scanning electron microscopy of fly artifacts deposited by Calliphora vomitoria (Diptera: Calliphoridae) on household materials

Abstract

Insects found at a crime scene can produce traces referred to as fly artifacts (FA) due to their movement over the corpse and the manner in which they feed upon it. These can be detrimental for carrying out criminal investigations. Confusing a FA with a genuine bloodspot can lead to misinterpretations, also taking into consideration that FA may contain a human DNA profile. The aim of the present study was to employ scanning electron microscopy (SEM) for the analysis of FA produced by Calliphora vomitoria on hard surfaces and fabrics that are commonly present at crime scenes. FA and control bloodstains were produced under experimental conditions on metal, glass, plaster, cotton, and polyester. After macroscopic analysis, FA were examined at standard low (20–40 ×), medium low (300–600 ×), and high ultrastructural (1200 ×) magnification through a SEM Stereoscan 360, Leica, Cambridge. SEM analysis enabled the identification of distinctive features of FA on hard surfaces, namely, amorphous crystals, micro-crystals with a morphology similar to those of uric or micro-crystals with a comparable morphology to cholesterol, absent in controls. Moreover, red blood cells (RBC) were absent in FA but were always present in controls. On cotton, for both FA and controls, the drop was almost completely absorbed and thus indistinguishable from the underlying fabric texture. On polyester, FA showed amorphous/crystal-like deposits and no RBC, as observed on hard surfaces, except for those showing a completely flat surface. SEM analysis appeared to be suitable for differential diagnosis between FA and genuine bloodstains on hard surfaces, although the results may be inconclusive on tested fabrics.

Distinction of Fly Artifacts from Bloodstains in Crime Scenes: A Brief Literature Review

“…RBCs were absent in fly artifacts. In their subsequent studies, artifacts from Calliphora vomitoria were analyzed on glass, metal, plaster, cotton and polyester [17]. Amorphous crystals, and/ or micro-crystals whose morphologies are similar to uric acid and cholesterol are confirmatory observations with FA.…”

The use of fly artifacts in a crime scene: Is there any application for forensic toxicology?

“…FA were experimentally produced by applying the methodology already described by our group [15,16]. Briefly, three identical scenes of 0.12 m 3 (1 × 0.3 × 0.4 m) each were produced, with surfaces covered with absorptive, that is, cotton-textile, and non-absorptive materials, that is, plastic and glass.…”

“…Toxicological data provided by the analysis of dark and light FA were kept separated and compared. Morphological aspects were not taken into consideration for this study [13][14][15].…”

“…The purpose of this study is to understand if FA trace evidence permits toxicological analysis when traditional matrices are not available. To this aim, an ad-hoc crime scene was ideated and created on the base of authors' experience [13][14][15] and Calliphora vomitoria specimen were then artificially introduced for 2 days. FA were then carefully collected from absorptive and non-absorptive surfaces and analyzed for drugs of abuse.…”