Importance of Calliphoridae Diptera In Forensic Science

Introduction

Diptera have colonised all kinds of habitats, both natural and anthropised. Many species are synanthropic, i.e., they live in close contact with humans and, among them, some can be used as indicators in criminal and civil proceedings. Forensic entomology is a field of zoology that, through the study of arthropods, their biological cycle, and their eco-ethology, is part of the judicial system, for the resolution of suspicious deaths, infestations, and in all cases of neglect and abuse of weak subjects (human and animal subjects) and incapacitated.

Adult Female may lay 100-200 eggs in cluster on a food source. 

The main objects of study in forensic entomology are the Diptera, belonging to the Calliphoridae, Sarcophagidae, Muscidae and Fanniidae families. The use of insects in forensic science plays a significant role in Italy. It is important, therefore, to expand and improve our knowledge of the species that can be used in investigative contexts.

The data on the spatial and temporal distribution of the insects, but also their thermal or altimetric range, allow accurate conduction of the crime scene and/or the judicial context under examination.

Also Read: How Insects Help Forensic Experts in Criminal Investigation?

Forensic Entomology

Forensic entomology is a discipline that studies arthropod species found on or near a corpse to reconstruct the crime scene, to date the time of death of the subject and to identify the cause of death and the offender. Insect species in particular collected on and around the body are useful evidence for judicial investigations.

The forensic entomologist plays a key role in the reconstruction of the crime scene by assisting the medico-legal examiner and the forensic pathologist both during the forensic investigation and during the autopsy examination. During the forensic investigation, the entomologist must examine the crime scene, the environmental context, the position and state of preservation of the body, the presence of fauna, both before and after removal of the corpse, and measure the environmental temperature at the time of the investigation. Therefore, the entomologist must estimate the time of death of a subject and verify whether the location where the corpse was found coincides with the location where the death occurred.

Role of Diptera in Forensic Science

Diptera play a critical role in forensic science because they provide a range of important information:

Blow Flow Larvae (Maggots) are yellowish-white with a tapered head and no head capsule.

They provide information useful for estimating the Post Mortem Interval (IPM); they indicate whether the body was moved or disturbed after death and, therefore, whether the place of discovery corresponds to the place where death happened; they provide information about the presence of wounds, following the atypical distribution pattern of larval masses; provide information on the victim’s intake of drugs or poisons; Diptera are indicators in cases of neglect or abuse of older people, children and living animals, and therefore also play an important role in assessing the ante-mortem living conditions of a subject. Insects that cause “miasigenic frameworks” are of great importance in forensic entomology because their presence on a living human body is often synonymous with neglect of hygiene and avoidance.

Entomological Successions

In many environments, insects colonise bodies almost immediately after death. Their development rate and the alternation of species over time can be used to accurately determine the time of death. From the moment of death, the body goes through different stages of decomposition and each stage is attractive to different insect species that colonise the bodies depending on the stage of degradation of the food substrate. The colonisation of the corpse by the different ecological categories of insects (necrophagous, saprophagous, predatory and parasitic, omnivorous, accidental) takes place in a predictable sequence but depends on the season, the geographical area, the location of the corpse (in the shade or in the sun, for example) and other factors intrinsic or extrinsic to the corpse itself (bodies clothed/undressed, buried, burnt or in water to name but a few cases.

Blow Flies have complete life cycle consisting of an Egg (8-12 hours), Larval (20-Several Days), Pupal (Average 5 days), and Adult (Several weeks) stages. 

There are five ecological categories of insects that can work on body:

1. Necrophagous species: they feed on the dead tissues of carcasses and constitute the most important category for death estimation. These include mainly the Diptera Calliphoridae and Sarcophagidae but also beetles belonging to the family Silphidae;

2. Saprophagous species: they feed on decaying organic material, such as flies belonging to the Muscidae and Fanniidae family but also the beetles Cleridae and Dermestidae;

3. Predators and parasites of insects and other arthropods: this category includes Staphylinidae, Silphidae, Histeridae and Hymenoptera. Some species begin their development as necrophagous, before becoming predators in their late stage of development, such as the dipteran Calliphoridae of the species Chrysomya albiceps;

4. Omnivorous species: they are not obligate necrophagous, but use the corpse as an available resource, as in the case of wasps and ants;

5. Incidental species: these are species specific to the crime scene habitat and only use the corpse as an extension of the habitat, i.e., collemboles and spiders.

Morphology of the Diptera

The Diptera order is subdivided into two suborders: the Nematocera and the Brachycera.

The Brachycera have a more robust and stocky body and short aristate antennae; they have bright colours or metallic highlights and a dense chaetotaxy, especially on the head and thorax. The head is well developed and is characterised by the presence of large eyes composed of a large number of ommatidia. The antennae, inserted on the head, have a sensory function. The buccal apparatus has a different structure and appearance, of the lambent-sucking or pungent-sucking type, and is aimed at the intake of sugary foods or semi-fluid foods such as excrement. The thorax houses the wings and the three pairs of legs. The wings are generally hyaline and characterised by the presence of ribs.

Brachycerous are holometabolous insects with complete metamorphosis and from the egg emerges a larva that will go through three larval ages and the subsequent pupal phase from which the adult will then emerge.

Diptera of Forensic interest in Southern Italy

Flies are the group with the greatest importance in the forensic field. Within this group of insects, the family Calliphoridae, represented by large, metallic blue-green flies, certainly plays a primary role.

Calliphora Vicina (Robineau-Desvoidy, 1830)

Length: 5-12 mm;

Wingspan: 13-27 mm;

Morphology: It is a large fly with a black head and yellow/ochre cheeks. The thorax is black-greyish with faint dark longitudinal stripes on the dorsal surface and is covered with a dense chaetotaxy. The abdomen is an obvious bright, metallic blue with silvery hues. The legs are black. It can be distinguished from other Calliphora species by its cheeks and orange anterior thoracic spiracles. Males of C. vicina have a wider interocular distance than males of other species.

Feeding: Adults visit the flowers of various plants, feeding on nectar and pollen (Asteraceae, Rosaceae, Salix aurita) and Phallus impudicus mushrooms. They are mainly attracted, however, to decaying matter, rotting fruit, rotting meat and excrement. The larvae are necrophagous and are mainly found on animal carcasses, especially mammals and birds.

Ecology: It is a cosmopolitan species that mainly prefers shady situations and urban habitats where it is dominant over human corpses. Adults are present all year round. It can be found in indoors during the winter and may be active outdoors on mild winter days, especially around buildings. In the southern United States it is considered a winter species, while a spring and autumn species in temperate zones and a summer species in subpolar regions. In southern Italy it is active all year round, except in the warm months, in rural and urban areas, while in forest areas it is mainly present in the winter season.

Forensic/parasitological field: it is an important species for forensic entomology and is often used in the estimation of IPM but is also known to be the cause of occasional myiasis in humans as well as in domestic and wild animals. In addition, it is a species used in toxicological analyses.

Also Read: How To Become Forensic Entomologists?

Calliphora vomitoria (Linnaeus, 1758)

Length: 8.5- 14 mm;

Wingspan: 20-28 mm;

Morphology: Distinguished from C. vicina by the black cheeks covered with thick orange hairs. Also in this species, the thorax is blackish with four faint dark longitudinal stripes. The abdomen is bright metallic blue with silvery highlights. The posterior margin of the abdominal tergites ranges from dark blue to black, often with a hint of turquoise. The legs of this species are black. Overall, the body appears very stocky and bristly.

Feeding: The adult feeds on the same substrates as C. vicina; the necrophagous larva feeds on animal carcasses, especially mammals and birds.

Ecology: This species is common in rural and suburban wooded areas, where it prefers shady conditions. It is dominant in heathland areas up to 700m above sea level in areas of England and Wales where it has been found on dead sheep. It is less synanthropic than C. vicina. In Britain it is mainly active from March to November and, as a larva, prefers conditions of high humidity. In southern Italy it is widespread mainly in forest areas and is present from May onwards; in rural areas at low altitudes, however, it is present from the winter period.

Forensic/parasitological field: the species of forensic interest is used in the estimation of IPM in different geographical areas. The species causes miasis in humans and various animals.

About The Author

Ms. Chiara Lucanto Has Master Degree in Forensic Biology at University of Calabria – Italy. She is also a PG Student at Bio Forensics Research Center. She is a Certified Specialist of “Forensic Biology Survey” – Accredited by FAC CERTIFICA (according to ISO 17024 standards).