Forensic Entomology

Chapter 1

The scope of forensic entomology

Forensic entomology is a branch of forensic science. Forensic entomologists use information about insect lifecycles and behaviour to help interpret evidence in a legal context relating to both humans and wildlife. On occasion, the term ‘forensic entomology’ is expanded to include other arthropods, mites, spiders, or macroinvertebrates such as freshwater shrimps. The legal contexts in which forensic entomology is of use relate to matters considered in either civil courts or criminal courts. The cases that are heard in civil courts most frequently relate to insect infestation in urban contexts or in relation to stored product pests. Where there is insect infestation of a body, either living or dead, and foul play is thought to have occurred, or a law has been broken, then the case is generally termed a medico-legal case. Such cases can relate to both humans and wildlife.

1.1 Forensic Entomology in Urban Contexts

Cases of infestation of homes or other buildings, such as hospitals, are instances in which forensic entomologists may have a role to play. For example, where structural timber is found to harbour insects such as longhorn beetles (Cerambycidae) an entomologist might be called to assist in determining the cause and source of infestation. Such insects are generally pests of sapwood, but can complete their lifecycle in dry wood that has been harvested. An example of such a beetle is Eburia quadrigeminata (Say), the ivory marked beetle, a longhorn beetle, which usually attacks living American oak trees but has been known to survive felling, wood treatment and transformation of the wood into furniture, only to emerge some 10 to 15 years later. In 2007, Cocquempot recorded an instance of this species having been caught when emerging from a bamboo stand in France.

Other examples of the urban application of forensic entomology relate to infestation of food premises and food production sites. For example, the owners of a butcher's shop in London, was closed in January 2010. The Magistrates' Court awarded costs of £560 to the council after meat on sale at the butchers had been found to be infested with maggots and fly eggs.

Poultry production units may similarly be convicted of causing fly infestations that affects residents living nearby. Such was the case in a small Lincolnshire village where, in 2009, the farm owners were fined £20 000 by Skegness Magistrates court, having pleaded guilty to breaching an abatement order, intended to reduce the numbers of flies, which had been put in place in 2008 for a similar misdemeanour.

1.2 Stored Product Infestation and Forensic Entomology

In general, only a small number of stored product pest species may be encountered by the forensic entomologist. They include flies, cockroaches, ants, and beetles. The insects that inhabit animal products and their waste include members of families such as larder beetles (Dermestidae), Moth flies (Psychodidae), Scuttle flies (Phoridae), Muscid flies (Muscidae) Blowflies (Calliphoridae) and Flesh flies (Sarcophagidae) such as Sarcophaga carnaria Linnaeus, ants (Formicidae) such as the Pharaoh ant (Monomorium pharaonis Linnaeus), or the Copra beetle (Necrobia rufipes DeGeer). These may also be cited in medico-legal cases (Figures 1.1 and 1.2).

Figure 1.1 Stored product pests

The following are examples of phytophagous insects, which may infest food, resulting in forensic entomologists contributing to court cases.

Biscuit beetles (Stegobium paniceum Linnaeus) will infest not only food items such as flour bread and biscuits but also wool, hair and leather material. The saw-toothed grain beetle (Oryzaephilus surinamensis Linnaeus) and the Indian meal moth (Plodia interpunctella Hubner) both infest dried fruit, breakfast cereals and pasta. The Indian meal moth is also known to consume dried dog food and fish food products. The rust-red flour beetle (Tribolium castaneum Herbst) and the confused flour beetle (Tribolium confusum Jacquelin du Val), infest grain and flour. The fruit fly (Drosophila melanogaster Meigen) will infest any fermenting fruit or vegetable, including tomatoes, onions, and bananas. It can also inhabit compost heaps and piles of rotting garden waste and so could be the subject of urban forensic entomology cases.

Because food-processing plants have difficulty in reducing insect infestation levels to zero, a legal tolerance level is specified in many countries, contravention of which can lead to prosecution. For example, the American Food and Drug Administration considers that, in canned citrus juice, a maximum of five or more eggs of Drosophila or other insects per 250 ml is allowable. The presence of one maggot per 250 ml of canned citrus juice is also considered acceptable (AOAC 970.72).

In the majority of instances in stored product and urban forensic entomology, the main focus of the contribution is confirmation of the identity of the insect species and interpreting its biology in the particular context in question. In such instances this aspect of forensic entomology is confirmatory and relates to the work of the Environmental Health Department or the Office of Trading Standards.

Figure 1.2 Insect structural damage to wood

1.3 Forensic Entomology in the Medico-Legal Context

Insects have a role in crime scene investigations on both land and in water (Anderson, 1995; Erzinçliolu, 2000; Keiper and Casamatta, 2001; Hobischak and Anderson, 2002; Oliveira-Costa and de Mello-Patiu, 2004: Moretti, Bonato and Godoy, 2011). The majority of medico-legal cases where entomological evidence is used are the result of illegal activities that take place on land and are discovered within a short time of being committed. In France for example, 70% of cadavers are found outdoors and, of these, 60% are discovered within less than one month (Gaudry et al., 2004).

Figure 1.3 Body in wrappings

All insects could be of potential relevance to a medico-legal question, however a number of species from several families are found more often than others. The insects of particular relevance to forensic entomological investigations include blow flies, flesh flies, cheese skippers, hide and skin beetles, rove beetles and clown beetles. In some of these families only the juvenile stages are carrion feeders and consume dead bodies. In others both the juvenile stages and the adults will feed on the body (are necrophages). Yet other families of insects are attracted to the body solely because they feed on the necrophagous insects that are present. Forensically relevant insects can be grouped into four categories based on feeding relationship. These are:

• Necrophages, which feed only on the decomposing tissue of the body or body parts – for example blowflies, hide beetles and clown beetles (Figures 1.4 and 1.5).
• Predators (and parasites) of the necrophages – for example rove beetles and ground beetles.
• Omnivores that consume both the live insects inhabiting the corpse and the dead flesh – for example ants (Formicidae), and wasps (Figure 1.6).
• Opportunist (adventive) species, which arrive because the corpse is a part of their local environment – for example mites, hoverflies, butterflies and, on occasion, spiders (Figures 1.7 and 1.8).

Figure 1.4 Necrophagous insects colonising a body

Figure 1.5 Predatory beetles will consume eggs and larvae of those flies colonising the body

Figure 1.6 Omnivores such as wasps will consume both the body and any insects present

Figure 1.7 Opportunist insects – a spider. Source: Reproduced by permission of Mr. Ian Ward

On occasion waste material or faecal material may be the attraction (Figure 1.8). The roles of specific species which have these feeding strategies will be considered in later chapters.

Figure 1.8 An opportunist butterfly attracted to faecal material. Source: Reproduced by permission of Mr. Ian Ward

1.4 The History of Forensic Entomology

Insects are known to have been used in the detection of crimes over a long period of time and a number of researchers have written about the history of forensic entomology (Benecke, 2001; Greenberg and Kunich, 2002). The Chinese used the presence of flies and other insects as part of their crime-scene investigative armoury and instances of their use are recorded as early as the mid-tenth century (Cheng, 1890, cited in Greenberg and Kunich, 2002).

Such was the importance of insects in crime-scene investigation that in 1235, a training manual on investigating death, Washing Away of Wrongs, was written by Sung Tz'u. In this early medico-legal book it is recorded that attention paid by a number of blowflies to a particular sickle caused a murderer to confess to murdering a fellow Chinese farm worker with that sickle.

Between the thirteenth and nineteenth centuries a number of developments in biology laid the foundation for forensic entomology to become a branch of scientific study. The two most notable were, perhaps, experiments by Redi (1668), an Italian who, using the flesh of a number of different animal species, demonstrated that larvae developed from eggs laid by...