“Forensic Entomology”
Introduction:
Forensic entomology is the study of insects associated with a human corpse in an effort to determine the time elapsed since death. Most cases using this technique are 72 hours or more old. Prior to 72 hours other techniques are more accurate than insect evidence. However, after three days, insect evidence is often the most accurate and sometimes the only method of determining elapsed time since death. An entomologist will always estimate a range of time for the death or PMI (post-mortem interval). This PMI will vary from a few hours for bodies that have been dead for a day or two, to perhaps several months for bodies that have been dead for several years.
There are two main ways of using insects:
1. Using the succession of different insect species.
2. Using the age and development of specific insect larvae.
The first method used is based upon the fact that the human body evolves from the fresh state to dry bones in a matter of weeks or months depending on geographic region. During this decomposition, the remains go through rapid physical, biological, and chemical changes, and the different stages of decomposition are attractive to different species of insects.
The second method can give a date of death accurate to a day or less and is used in the first few weeks after death. Insects like Blowflies, are those that arrive first on the corpse. They are attracted to the corpse soon after death and lay their eggs on the corpse, usually in a wound or a body opening like the mouth, nose, eyes, ears, genitalia, or wounds. The development of the eggs and other stages follows a set, predictable cycle.
“Forensic Entomology”
Objectives:
· Extracting factual information from text
· Making logical deductions from information presented
Scenario:
A body has been found near a sheltered watering hole in the Australian outback. You and your investigation team have been called in to determine, among other things, the approximate age of the corpse. By the time you arrive most of the Blowflies have come and gone, but many other insects are busy with the body. One of your colleagues notices Hide Beetles and Carcass Beetles. These creatures prefer their food source slightly dried, a condition quickly and easily accomplished in the outback. Although dead, the body seems almost alive with activity. Much of the surface appears to be moving. Your eyes are drawn toward the numerous glitters of deep red. You lean in closer and immediately identify these miniature stop signs to be the heads of dead Rove Beetles. The Rove Beetles arrive early in the decomposition cycle but their larvae do not appear until a few weeks into decomposition cycle. These numerous larvae not only feed on the corpse but serve as a food supply for the Carcass Beetles as well.
It started to look like this body had been near the watering hole for some time. Additional evidence was provided by the presence of a Hairy Maggot Blowfly, Cheese Skipper Larvae and Black Soldier Fly Larvae both in the third instar.
The Challenge:
· Create a data table to organize your observations
· Using your evidence as support, prepare a concluding statement that determines the PMI.
· Using the information from the scenario, and the insect review cards, make a reasonable estimate of how long the body has been dead. Your concluding statement must make reference to the data you collected.
Forensic Entomology Insect Cards
Carcass Beetles:
Carcass Beetles are large beetles with very thick exoskeletons and uniform dark coloration. They are among the last beetles to inhabit a carcass as early as 2 months and as late as 4 months. They feed on dried remains such as skin, hair, and ligaments. Both adults and larvae feed on the carcass and the larvae live in vertical burrows underneath the carcass when they are not foraging.
Rove Beetles: The family of Rove Beetles is usually elongated beetles with small wing covers and large jaws. Like other beetle species inhabiting carrion, they have fast larval development with only three stages. The adults are early visitors to a corpse but the first instar larvae do not appear until about 3 weeks after decomposition begins. This time lag is due to the long development time of the egg. It is therefore common to observe the Rove Beetle larvae during the later stages of decomposition.
Cheese Skipper Flies: Cheese Flies get part of their name because they are attracted to the cheesy odor which emanates from a corpse during the later stages of decomposition, particularly when the body is undergoing butyric fermentation. The adults may arrive within the first week but the larvae only begin to appear after the second month. The “skipper” part of their name describes the behavior of the maggots. When disturbed the larvae flex and release their bodies, skipping 15 cm into the air. Cheese Skippers have been found in coffins buried up to 3 m deep and in corpses up to 10 years old.
Blowflies: Often an attractive blue-green, metallic color, blowflies are relatively large. They pick up the faint odors of decay and can fly up to 20 km from their birthplaces in search of a suitable corpse in which to lay their eggs (which take 16 hours to develop into the first larvae stage). The larvae go through three instars (molts). The first lasts about a day, the second about 20 hours, and the third about 4-5 days. It takes about 16 days for it to complete its life cycle from egg to adult. Maggots are of two forms: smooth and “hairy.” Smooth maggots belong to the pioneer flies and are purely corpse feeders. “Hairy” maggots often feed on corpses, but are also active predators, which also feed on the smooth maggots.
Hide Beetles:
Hide Beetles are some of the most important animals present in the final stages of decomposition of a carcass. The adults and larvae are not predaceous and feed on the dried skin, hair, tendons, ligaments, and bone left by the fly larvae. Hide beetles are the only insects with the enzymes necessary for breaking down keratin, a protein component of hair. Hide Beetles and Carcass Beetles can often be found together on the same corpse.
Black Soldier Fly:
The adult Soldier Flies are generally 1.5 cm long with smoky black wings that are held back when at rest. They resemble wasps but have no stinger and are harmless and are relative late comers to a decaying corpse generally arriving three to four weeks after the time of death.
The larvae of the Soldier Fly are torpedo-shaped and flattened with skin that appears firm and tough. Like other insects, the larvae pass through three instars each lasting approximately two days.
Carrion Beetles:
Although they often hide under a carcass the Carrion Beetle often be seen wandering around a decomposing body with a maggot in its mouth. Even though adults have been seen feeding on a corpse they cannot survive on it alone and must have access to larvae. These beetles often arrive after the second week and remain as long as their main food source is plentiful which usually lasts between 33 and 45 days. Then corpse at this point is almost reduced to hair and bones.