Commentary on: Rivers DB et al. Immunoassay detection of fly artifacts produced by several species of necrophagous flies following feeding on human blood. Forensic Science International: Synergy 2019;1(1):1-10.

While the article is interesting from the perspective of scientific inquiry, it is disappointing to learn that the federal government would squander financial resources on research that seemingly possesses little-to-no practical value at scenes. The United States Department of Justice, through the National Institute of Justice, provided over $150,000 of support for this well-intentioned, but misguided, project. Unfortunately, the authors’ primary opinion for the necessity of this study is incorrect.

Statements made in the published research and the NIJ Award notice contend that scene artifacts produced by flies cannot be differentiated from traces that originate from airborne blood drops. The authors state, “The issues with fly artifacts are magnified by the fact that stains from regurgitation and fecal elimination are virtually indistinguishable from human bloodstains” [1]. In the NIJ Award 2016-DN-BX-0181, Development of a Quantifiable Confirmatory Test to Detect Fly Artifacts Contaminating Bloodstain Evidence, they proposed: “Presently there are no methodologies for distinguishing contaminating insect artifacts produced by flies or other insects that visit and feed on a corpse from stains derived from human body fluids. In fact, artifacts derived from common flies are indistinguishable from bloodstains, particularly those associated with high impact or projected blood spatter” (emphasis added) [2]. While this assertion may be true for scattered or lone dark-red deposits, it is not true for traces that may otherwise be “misclassified” as patterns resulting from airborne blood.

Traces created by various species of flies, which are comprised of putrefaction fluid and/or blood post-ingestion, are readily identifiable as an artifact by educated and experienced criminalists. Trace colors vary from dark red to light brown (i.e., beige) and many possess “tails” oriented in random directions, unlike those typically observed in patterns of spattered blood. Fig. 1, Fig. 2 illustrate a typical pattern of “fly artifacts,” traces produced by flies near a wall lamp; such patterns would be nearly impossible to misclassify, even by a novice. Interestingly, the study's authors chose to include color-desaturated images, thereby, limiting the reader's ability to use this feature to assess their illustrations. To experienced criminalists, the pattern depicted in Fig. 1 in the article would not be misclassified as deposits of spattered blood [1].

Fig. 1

Traces, so-called fly artifacts, produced by flies. Traces reside on the wall in the vicinity of an incandescent wall lamp (powered off for the photograph).

Fig. 2

A closer view of traces, so-called fly artifacts, produced by flies. Traces reside on the wall in the vicinity of an incandescent wall lamp (powered off for the photograph).

Viero et al. and Zuha et al. have previously reported on the morphological characteristics of traces produced by flies [3,4]:

Blood Traces

Same color and/or shade of color

Trace morphologies are circular and elliptical

Morphology correlated to the incident angle

Traces appear to radiate from a common origin

“Fly Artifacts”

Different colors and/or shades of colors

Defecation spots (creamy, brownish, and dark)

Regurgitation (“craters” with lighter centers and darker perimeters)

Trace morphologies are irregular and variable

Random orientation of “tails”

Absence of area of convergence

Durdle et al. described several additional features [5]. Misclassification of patterns can be avoided with a rigorous scientific approach: the careful examination of all traces; the consideration of all relevant scene information, data, and physical evidence; and a criminalist with the appropriate education, training, and experience; Viero et al. and Emes & Price implied use of a similar strategy [3,6]. Shaler also suggested that “fly artifacts” should not confound bloodstain pattern analysts [7].

Trace color and morphology, a sufficient quantity of traces (i.e., a pattern), the location of traces, and evidence of flies are often required for the classification of a pattern of deposits as “fly artifact.” Generally, these patterns are encountered when significant insect activity is apparent, most often in cases involving decomposing bodies. A few clustered, dark-red deposits can prove problematic; however, such patterns generally should not be categorized beyond a description. Attempts to determine the mechanism of deposition for a few scattered, essentially lone, dark-red deposits should not be attempted without caution, consideration of alternative hypotheses, and additional laboratory analysis.

In summary, governmental agencies should use more discretion when spending monies, which have been collected from taxpaying citizens. While interesting, the present study has little potential for use in the field and limited potential in the laboratory.