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

A literature search in the electronic databases Pubmed, Scopus and Web of Science was conducted using a combination of free text protocols (i.e. “insects”, “flies”, “artefacts”, “post-mortem”, “forensic”, “crime scene”, “body”, “blood”, “stains”) individually combined through the Boolean operator “AND”. At the same time, filters such as full-text, publication date from January 2000 to September 2016, and English language were activated resulting in more than 100 articles, which were submitted to the following criteria of inclusion (one at least):

Moreover, entomological books and forensic entomology and pathology manuals [7‐12], which include chapters dedicated to the description of post-mortem artefacts in death scene, were also included.

Subsequently, the selected papers were analysed in full text together with the chapters of the selected books and manuals.

Bloodstain pattern analysis (BPA) has a key role during crime scene investigation, providing crucial information about the physical events that led to the bloodstain deposition [49]. The information obtained by BPA can be used for the reconstruction of the manner of death and the evaluation of other primary issues related to the death, such as the victim’s and perpetrator’s position and movement before and after committing the crime and the assessment of witnesses’ statements [48].

Since bloodstains are not static and can be altered after formation, in particular during the liquid phase, some alterations after deposition should be considered as part of the BPA (i.e. transfer, contact and drip patterns, expired blood or high velocity spatter), and they could allow the reconstruction of the criminal acts [19, 48, 51]. Problems can arise when other modifications, such as those produced by the insect activity, alter the bloodstains and consequently their interpretation. These alterations are commonly defined fly artefacts (FAs), when produced by the action of blowflies, or, more generally, insect stains [52].

Morphological alterations of bloodstain pattern due to insect activity are described in several entomological textbooks [7‐9], but, until now, few real cases have been reported in the forensic literature [22, 37, 47, 53, 54]. This discrepancy could be due to a lack of consciousness regarding the ability of insects to alter the death scene, producing artefacts that could be misinterpreted as bloodstains produced during the crime.

FAs were described for the first time by Lassaigne in 1856 [55], who defined them as small stains transferred from a blood source to a blood-free surface by the action of blowflies. FAs are produced by the tarsi of flies, that come in contact with a blood source, so that blood-soaked tarsi can get in touch with any surface [7]. Contamination can also be the result of the digestive process, because of the nature of the fly feeding, consisting in a first extra-oral digestion due to the excretion of some enzymes, followed then by the ingestion of the food in a liquid state. Blow flies ingest blood using a sponging mouthparts and then regurgitate the ingested food by partially expelling it as a bubble and then sucking it back in. In addition, flies can also defecate material derived by the digestions of blood or decomposing fluids on the crime scene [8].

The differentiation between FAs and bloodstains and the confounding factors affecting their shapes and characteristics have been widely discussed in forensic literature [47]. Benecke et al. [22, 56] reported three cases in which differential diagnoses between bloodstain patterns and FAs were crucial in determining the manner of death. The same authors described some features of FAs (e.g. stains that have a tail-to-body ratio greater than 1, stains with a tadpole/sperm type structure, stains with a sperm cell-type structure that do not end in a small dot. stains without a distinguishable tail and body, stains that do not participate in directional consistency with other stains that suggest a point of convergence at a point of origin) that can be useful for distinguishing the FAs from the bloodstains. However, these features are still the matter of debate [53, 57].

The same authors [22] also provided general rules to be followed during crime scene investigation, including the documentation of fly activity and of the range of stains. They reported as well how to compare the FAs observed on the crime scene with other known fly artefact patterns. They concluded that the presence of spots far from sources of blood is not suggestive of a bloodstain because blowflies are able to deposit FAs also in room in which blood is not present [25]. When dealing with a group of spots, the comparison among the droplets pertaining to the same pattern can be a useful method for the distinction between bloodstains and FAs. Laboratory analyses performed on different species of blowflies showed that FAs are characterised by a wide range of size, shape, reflectance, lack of congruent directionality or consistent colouration and a distribution that appears evenly spaced [37]. One of the indicators used to distinguish FAs from bloodstain is that artefacts have tails going in directions that were contrary to the majority of drops [25]. Blood ingested by flies is not completely digested before defecation and may even pass through a fly digestive system without any degradation. For this reason, faecal matter resembles to blood both from a biomolecular and chemical point of view: these artefacts contain enough human blood to give positive results with haem-based presumptive tests [25, 42, 50]. As a result, chemical and chemo-fluorescent presumptive blood tests are unable to distinguish blood from FAs so they have to be used with caution/attention before making any hypothesis. Immunological confirmatory tests (which detect the presence of haemoglobin) have been demonstrated to be more useful, being able to distinguish between 3-day-old artefacts from blood, and less reliable in the differentiation between 2-week-old artefacts from biological fluid [41]. However, some differences were observed between the manner of deposition, and consequently the appearance, of FAs, even between different species. The surface can also influence the deposition and, consequently, the shape of FAs. As an example, the so-called “carpet avoidance behaviour” implies that on a few fly stains are observed in crime scene where blood pool or stains occurred primarily in porous surfaces, such as carpets [43]. Moreover, porous surfaces can modify the deposited morphology of artefacts or bloodstain, so that investigators have to be aware of potential contamination by FAs when looking at drops on clothing, carpet or other porous and irregular surfaces [37].

Even if there are not universal rules that can be used to differentiate FAs from bloodstains, Table 1 summarises some characteristics that could suggest the origin of a suspicious spot or group of spots.

In addition to macroscopic observations, immunological and molecular tests have to be applied for the correct identification of suspect spots [35].

On the other side, flyspecks can be a further source of human DNA useful for victim identification if the body is removed from the crime scene before the investigators’ arrival. From this point of view, flies can be considered as a vehicle for the spreading of the victims DNA. Human DNA can be extracted from FAs in sufficient quantities to provide a full profile of the donor [27‐30, 34, 41]. The amount of DNA that can be extracted, and so the number of FAs required to generate a forensic relevant profile, depends on the biological material ingested by the fly (i.e. blood, semen, saliva) [30]. DNA can be extracted from FAs derived from blood and semen for a period of at least 2 years, and from saliva for 2 months after deposition [27, 28]. As a result, artefacts can be a valuable source of DNA for investigators in cases where the victim’s body was removed and/or the offender attempted to clean up any biological evidence due to the ability to be sampled a long time after deposition and far from the crime scene. This last event can be also considered as a potential source of contamination, and particular attention has to be paid in case of an exogenous DNA profile is found in a crime scene.

Diptera larvae, called maggots, in the families Calliphoridae, Sarcophagidae and Muscidae are the primary consumers of animal organic matter. After completing their feeding phase, the majority of the larvae (e.g. Calliphora spp., Lucilia spp., etc) disperse to find an adequate place for pupariation and then pupation (the final developmental stage of metamorphosis into the adult stage) whereas a minority remain on the corpse or in the clothes (e.g. Phormia regina and Protophormia terraenovae). This phase of wandering larva is called “postfeeding” because at this stage, larvae stop feeding and empty the digestive system from any food remains [54] (Figs. 1 and 2). Larvae can migrate up to 10 m from the body, towards sheltered areas [8, 58]. During this process, if migrating from a surface soaked by blood or putrefactive liquid, maggots could leave a linear wipe pattern, resulting in a series of trails produced by their typical crawling motion. This pattern could be misinterpreted as an attempt to move the body, as a wipe pattern produced by third subjects or by the victim itself in the dynamic of the crime/death (e.g. swipe patterns created by bloody hair) (Fig. 1).

Not only fly maggots but also cockroaches, through the action of their tarsi, can produce blood-like droplets. They are larger than those produced by blowflies and consist in a series of tracks that often have a centre drag mark or “smear”, caused by the cockroaches dragging its abdomen [7]. The main differences with FAs are that patterns produced by blowflies are isolated, smaller and not as uniform [7]. Artefacts produced by cockroaches, due to their discontinuity, are also easily distinguishable from that produced by larvae.

In forensic investigations, the estimation of the origin and the age of ante- and peri-mortem injuries is one of the fundamental steps to identify the cause of death [35] that, as previously mentioned, is one of the key points for crime reconstruction. Moreover, after death, corpses go through a series of transformations and alterations resulting from cellular and tissue lysis, from seaweed, fungi and plants proliferation and from local macro- and micro-fauna feeding activity [16, 39, 46]. In particular, faunas, both micro (e.g. insects) and macro (e.g. carnivores and other scavengers), play an important role in the flesh removal causing different kinds of macroscopic alterations of the body.

This kind of post-mortem alteration deserves the forensic pathologist’s attention when evaluating corpses either at the crime scene or during the autopsy [35]. In fact, the underestimation of such alterations may cause considerable complications in clarifying the cause of death, leading to wrong conclusions [59].

In particular, post-mortem damage of tissues may result in lesions that resemble inflicted or accidental ante-mortem injuries (Fig. 3). Furthermore, the post-mortem body alterations can cause modifications of the real ante-mortem wounds (i.e. pattern, size, shape), with loss of identifying features and damage or removal of internal organs [36].

The scavenging activity varies considerably depending on the animal feeding on the body with variation associated with the region, the season and the environmental conditions [16] and sometimes the distinction between ante- and post-mortem injuries is very difficult to be detected.

In particular, insect artefacts can take place on superficial ante-mortem injuries, resulting in the modification of wounds and/or loss of identifying features, for instance a gunshot wound or even more nail abrasions in the neck after manual strangulation [39].

Furthermore, injuries resulting from post-mortem arthropod activity can confuse even experienced pathologists in terms of the nature and chronology of the injury, due to similarities with the ante-mortem wounds so that they may be misidentified as sources of intravenous drug use, bite marks, defensive wounds, ulcers, burns or abrasions, signs of an attack, abuse, neglect or torture or other activities depending on the case and death scene circumstances [35, 38].

Regarding post-mortem arthropod activity, the alterations can be divided according to the affected tissues and, for each tissue, according to the type of arthropods involved (Table 2).

Among the arthropods, the most abundant species active in the body decomposition belong to the orders Diptera and Coleoptera [35, 36]. However, the arthropods described in the literature as causes of skin and soft tissues alterations that may be confused with ante-mortem injuries are ants (Hymenoptera, Formicidae), beetles (Coleoptera) and aquatic organism (e.g. Crustacea, Isopoda and Amphipoda) and the main literature on this topic concerns case reports [13‐17, 20]. In addition, in the last year, a case of injuries on pig skin was reported from a forested area in Chile as caused by scorpion flies in the family Eomeropidae (Mecoptera) [60].

On the contrary, despite the large diffusion of cockroaches (Blattodea), especially in degraded and dirty environments, little information is reported about their activity on the bodies.

A variety of insect taxa can modify bones with their mandibles, including the larvae and adults of some beetles (i.e. Dermestidae, Tenebrionidae, Scarabaeoidea), moths (Tineidae), wasps (Halictidae, Sphaecidae) and termites (i.e. Termitidae, Mastotermitidae, Rhinotermitidae) [31], as observed upon human remains in archaeological contexts [40].

In particular, terrestrial invertebrates, which have an osteophagic behaviour, can colonise the burial place and influence the taphonomic processes [24] even in completely skeletonized bodies, with destruction of bones associated with different forms of star shaped features, clusters of microscopically visible sub-parallel striations, edge gnawing, pits, holes, nests, tunnels and etching of the bone surface [21, 33]. Such holes can be misinterpreted as gunshot entrances.

Hairs are the most resistant structures in the human body after teeth and bones and nails and can be collected from a crime scene several years after a victim’s death. However, they can be altered by different organisms, such as fungi and arthopods, mainly insects in the orders Coleoptera and Lepidoptera. A general classification of damage has indicated that insect feeding activity only produces concave lesions caused by their “gnawing” activity, whereas fungal alteration leads to transversal tunnelling inside the hair structure. Studies of trauma on hair are extremely rare but a pilot study highlighted that the effect of the entomological components involved seems to be clearly distinguishable (thanks to the “gnawing” pattern) from sharp force trauma [44].