Table 1.

Features that can suggest the nature of suspect blood spots found during a crime scene investigation. In case of a group of spots, differentiation between bloodstains and FA relies on the comparison between the suspect spot(s) and other spots belonging to the same pattern. In case of a single spot, the differentiation is based on the assessment of some particular features that could be the result of fly activity. In both cases, there are not universal rules that can be followed for the distinction between bloodstain and FAs, solely based on macroscopic examination of the spots

Multiple spots		Single spot
Bloodstain Pattern [22, 37]	Fly artefacts [22, 25, 37, 48]	Bloodstain pattern [37]	Fly artefacts [22, 26, 37]
Same colour and/or shade of colour	Different colour/colour shade	Spines/scalloped edges	No distinguishable tail and body
All spots of elliptical/circular shape	Different/irregular shape	Linear and/or multiple tails	Curved or non-linear tail
Relationship shape/impact angle	Tails with opposite directions	Body length > 20 mm	Tail longer than body with irregular morphology
Consistent directionality	Random directionality		Textured surface
Radiating pattern	Absence of a point of convergence		Cratered appearance
Linear/curvilinear orientation			Evidence of flow