An Introduction to Forensic Entomology

Jobs for entomologists outside of academia are mostly in the agricultural or educational sectors, but there is one career that tends to be forgotten: forensic entomology. The most famous forensic entomologist may be CSI: Las Vegas‘s Gil Grissom, but it is in fact a very active field in real life, both practically and in research.

The forensic entomologist will typically be tasked with finding the time of death of a victim (Bugelli et al., 2015). Just like any new ecological succession, e.g. forest recovery after a fire or a whale carcass’s fall to the ocean floor, there is a specific order in which insects colonise a dead body. When the forensic entomologist is called to a crime scene, they will collect the insects from the dead body and calculate the time of death based on the species found, their developmental stage, and their abundances. Most often though, the coroner will send insect specimens if time of death couldn’t be determined from the liver.

Of course, things in practice are nowhere near as simple, with environmental factors, like temperature and humidity, significantly complicating things (Villet & Amendt, 2011). Even presence or absence clothing can be an important factor, since clothes provide an ideally wet microhabitat for insect development on a decaying body (Anderson, 2010). This is where experimental research comes in, usually done with pig carcasses (Catts & Goff, 1992) or human bodies in a body farm. I know a forensic entomologist who collects roadkill whenever driving around. Needless to say, he has no close friends.

This research looks at both the carcass’s decomposition process and the associated insects, as well as the biological development of the insects. Knowing the developmental rate of a species’s larvae is often more important information than the overall insect community.

More exotic cases abound, such as using bite marks on a suspect to tie them to a specific crime scene (Keh, 1985). A geographically-limited species found on a body proves that the body was moved, allowing a forensic entomologist to narrow down the location of the original crime scene (Benecke, 1998). Modern forensic entomological practice can even be used to find out what drugs a victim may have had in his body prior to death; this is a subfield called entomotoxicology, and it is quickly gaining prominence as drug overdoses continue to rise as causes of death (Verma & Paul, 2013). Cases of criminal neglect of children or the elderly can also be bolstered using forensic entomology (Benecke et al., 2004). Basically, insects can provide a lot of information if their presence is interpreted by an expert.

If you’re interested in becoming a forensic entomologist, then there are a few insect groups you should definitely specialise in. If in doubt, just become a dipterologist – muscoid flies can make up to 90% of the decay succession (Ramos-Pastrana et al., 2014), and they most often are the first to appear on a body and the last to leave, and are the highest tissue consumers (Archer, 2003). The most significant aspect of being a forensic entomologist is being able to make solid taxonomic identifications, not as easy a task as a start might think (see Grella et al. (2015) for an example).

Besides taxonomic expertise, as a forensic entomologist, you need to be excellent in collecting and laboratory methods. Identification of the insects as maggots requires precise measurements and sometimes molecular data (Sharma et al., 2015), and all this must be done in a very meticulous fashion so the evidence is valid in court and meet the Daubert standard, so you will need to know exactly how to preserve any insect you find in a way that their morphology doesn’t get distorted and DNA sequencing is still possible. Most often, larvae are reared to adulthood to be more easily identifiable, so a forensic entomologist also needs to know how to take care of a terrarium.

If you’re into forensic entomology but not into getting a secure career, you can specialise in archaeoentomology, the study of fossil insects related with archaeological human remains, giving insight into extinct cultures’ treatment of cadavers.

Forensically-important insects come in four ecological categories:

  • Necrophagous insects that feed on dead tissue;
  • Predators and parasites that attack all the other insects on the body;
  • Omnivores that feed on both the corpse and other insects present; and
  • Incidental, non-specialised species that are on the body just because it’s in the area.

As I said, the most important insects of forensic importance are, by far, the Diptera, specifically three families:

  • The Calliphoridae (blowfly) species belonging to the subfamilies Calliphorinae, Chrysomyinae, Luciliinae, and Toxotarsinae, are arguably the most important insect group for the forensic entomologist to be able to identify. As adults, they are frequently the first visitors to a body thanks to their great sense of smell allowing them to detect a decaying body within minutes (Sukontason et al., 2007). They lay eggs, and the maggots that hatch from them become the most voracious tissue feeders, going through two larval instars before migrating away from the body to pupate. The bulk of species-specific forensic entomology research has been done on calliphorid species, to the point that there are even developmental atlases available for forensic use (Brown et al., 2014).
  • Sarcophagidae (flesh flies) are found on any body at any stage of decay.
  • Muscidae (house flies).

Of course, many other fly families can be present, such as members of the Piophilidae (cheese flies), whose adults can be found during the bloating stage (Castro et al., 2012) and larvae on the dry remains (Grisales et al., 2010). Phoridae (coffin flies), Spaeroceridae (lesser corpse flies), Fanniidae (lesser house flies), Sepsidae (black scavenger flies), Heleomyzidae (sun flies), Stratiomyidae (black soldier flies), and Psychodidae (moth flies) complete the list of the most important forensic flies.

Next on the importance scale are beetles. While Diptera are always the first on the scene, if a body has been decomposing for weeks or months, then beetles are much more useful for determining time of death (Castro et al., 2013). The families you should specialise in are the Cleridae (ham beetles), Dermestidae (skin/hide beetles), Histeridae (hister beetles), Scarabaeidae (scarabs), Silphidae (carrion beetles),  Staphylinidae (rove beetles), and Trogidae (carcass beetles) (Horenstein & Linhares, 2011). Some beetles are among the first responders, appearing just after blow flies, while the Cleridae are among the last of the decomposers, one of the few insects capable of digesting keratin and thus speed up skeletonisation (Schroeder et al., 2002); they are also used in museums for cleaning skeletons). Other families of potentially regional importance are the Carabidae, Hydrophilidae, Leiodidae, Anthicidae, Nitidulidae, Rhizophagidae, Ptinidae, Tenebrionidae, and Geotrupidae (Smith, 1986).

Similarly, Tineidae moth caterpillars feed on mammalian hair and may also be present in the last stages of decomposition.

Outside of insects, mites can also play a significant role. Macrocheles mites are very common at the start of decomposition, and Tyroglyphidae and Oribatidae can be seen on dry skin nearer the end of decomposition.

If all this sounds exciting, a new academic book has been recently published: Forensic Entomology: International Dimensions and Frontiers (Tomberlin & Benbow, eds.; CRC Press). My cursory readings of it indicate that it’s a comprehensive look at forensic entomology’s history and status in major countries, combining real cases with first-hand insights of researchers and practitioners. It also delves into the future of the field, and so as a whole package, it is ideal for anybody seriously considering forensic entomology as a career choice. Below is the link to buy it.

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