Forensic Entomology

Forensic entomology is described as ‘the branch of forensic science in which information about insects is used to draw conclusions when investigating legal cases relating to both humans and wildlife although on occasion the term may be expanded to include other arthropods.’

There are many different aspects of forensic entomology including estimating time since death, identifying whether or not a body has been moved from a previous location, establishing whether drugs and toxins were an aspect of the crime and wound identification. Due to there being such a wide variety of topics within forensic entomology this essay will be focusing on estimating time since death of a body that has been left in the open. Bodies that have been buried or tightly

wrapped will have a different cycle of insects that colonise it.
Forensic entomology can be very useful when estimating time since death if it has occurred after 72 hours when all other indications are no longer able to be used.

This can be attributed to the predictable life cycle of the insects as well as their eating preferences as decomposition takes place. It is very common for the first insect to arrive at the body to be a blowfly, some even appearing just 10 minutes after death. The lifecycle of the blowfly is very predictable, and minimum time since death can be estimated by looking at the different stages that the larvae is at. The first stage initially begins with the female blowflies that have arrived at the body laying their eggs in the body’s natural orifices as well as any open wounds on the body. These eggs can also be identified as blowfly eggs before they hatch due to their characteristics of being white and very shiny, with an estimated length of between 0.9mm and 1.50mm and an estimated width of between 0.3mm and

0.4mm.
Once the eggs have hatched into the larvae there are three stages known as instars that they go through before being a blowfly. The first instar is what appears out of the eggs and is the smallest of the three measuring under 2mm in length and will stay this way for 1 and a half to two days. The second instar larvae with range from approximately 2mm-9mm in length which can take up to two and a half days with the third instar measuring between 9mm and 22mm and will stay this way for four to five days.
Despite these approximations the size of the larvae is not the most reliable way to determine which instar the larvae is in as a larvae with better access to food and nutrients will grow much larger than a larvae without.

Another more reliable way of determining age would be by looking at the slits that have formed in each of the posterior spiracle. The first instar larvae will have one slit, the second will have two and the third will have three.

Approximately half way through the third instar the larvae must being preparation for the pupariation stage where the larvae will make the transition from larvae to blowfly. To do this they stop feeding on the body and begin to move away in search of a dark, cool area and are often found to have buried themselves within soil (if present) reaching approximately 2cm-3cm down. This is commonly known as the post feeding and wandering stage of the third instar. Depending on the environment of the crime scene some of these larvae have been found up to 30 meters away from the body in an attempt to find a suitable

area.
Once the larvae has begun pupariation the puparial case in which the larvae resides in will slowly change colour until it becomes dark mahogany brown or black. Once it is time for the fly to emerge it uses its ptilinum, which is just a part of the head that becomes inflated with blood, to push its way out. When the fly first emerges it is unable to fly or expand its wings until it has dried out. The time in which it takes to dry out will depend on the temperature and this will need to be considered when establishing minimum time of death. This is the last stage in which minimum time since death can be estimated as it is difficult to tell the ages of adult blowflies.
The time of year will also have an effect on when the insects colonise the body with an increased amount of blowflies appearing in the summer. However during winter there would be a reduced number of blowflies if any at all. They will begin to properly colonise the body in spring.
Blowflies however are not the only insects attracted to decomposing bodies. Along with the blowflies appearing quite quickly flesh flies and ants will also be present between approximately the first and fourth day of death. After the fourth day all the eggs that the blowflies have laid will have hatched and making their way through their life cycles. Carrion beetles, hister beetles and assassin bugs will also be present after approximately the fourth day however this is to initially feed on the larvae as opposed to the body. These beetles prefer the body to be more decomposed before they begin to feed off it, with the nails, hair and skin all being dried out.
After approximately 8 days of decomposition scarab beetles, cockroaches and muscid flies will be present as they prefer to eat the body at this stage of decomposition. If these insects are on the body it indicates that time of death occurred roughly between 8 and 18 days before.
As the body decomposes further mites, springtails, cheese skipper flies and fruit flies will be present on and around the body. If these are found it can indicate that the time since death has been between approximately 19 and 30 days. After 31 days of decomposition there will be soldier flies and ground beetles found on the body.