How are insects connected to forensic science?

As the age-old phrase from the "Book of Common Prayers" reminds us, "Ashes to ashes, dust to dust." Often heard at funerals, it symbolizes life's cyclical nature, where humans transition from birth to death and from growth to decay. Forensic scientists and criminal investigators, however, might have their own variation of this saying: "Ashes to ashes, dust to bug food."

When forensic experts investigate a sudden, unexplained death, they carefully examine clues to reconstruct the event. The questions are many: What took place here? Who is responsible for this crime? Why did it occur? What tools, methods, or weapons were used? When did the event unfold? Drawing from a wide range of scientific disciplines, including biology, chemistry, physics, anthropology, and mathematics, trained professionals analyze all available evidence—whether it's shattered glass, dirt, bodily fluids, or any other trace materials—to craft an accurate narrative.

Typically, when we picture a crime scene, we envision yellow police tape, chalk outlines, shattered glass, and bloodstains. However, one often overlooked yet crucial element found around a victim's body during an investigation is a living organism—specifically, insects. Their presence often signals the aftermath of a crime.

What insights can bugs provide about death? How much can they disclose about a crime scene? And beyond just legal cases involving death, is there any other way forensic entomology can be helpful? Discover how bugs contribute to solving crimes while also enjoying a tasty snack on the next page.

Forensic Entomology - Bugs and Bodies Go Together

Just like flies swarm over a piece of decaying meat left out on a table, necrophilous insects, or flesh-eating bugs, are often linked to human corpses. Forensic entomology, the application of insect evidence in both criminal and civil cases, plays a crucial role in helping law enforcement and investigators uncover key details about what occurred to a body.

The primary branch of forensic entomology dealing with violent crimes is known as medicolegal entomology. It is also referred to as forensic medical entomology or medicocriminal entomology due to its focus on such crimes. Professionals in this field typically aim to determine several critical factors:

Insects found in the openings of a deceased human body, such as the eyes, nose, ears, and mouth, will typically arrive very quickly. Most insects can detect the scent of decaying flesh within hours of death, and certain insects, known as carrion insects, spend their entire life cycle feeding on dead flesh and producing new generations. Adult carrion insects, now mature and capable of movement, will fly to the nearest body to deposit their eggs inside.

Indeed, one of the most crucial facts an entomologist considers when investigating a death is that insects grow and develop within a corpse. Generally, an insect goes through three stages in its lifecycle inside a dead body. The first stage is the egg stage, where the insects are still contained within their eggs; the second stage is the larval stage, where the small, white larvae that have hatched from the eggs begin to feed on the dead flesh; and the final stage is the pupal stage, which is an intermediary phase before the insect becomes a mature, winged adult.

If an entomologist collects insects from a corpse during any of these stages—egg, larva, or pupa—and understands the insect's lifecycle, they can determine an accurate time of death. In other words, the entomologist must know two key facts: when the insect eggs were laid after death, and how long it takes for the insects to develop. These details help provide a precise estimate of how long the person has been dead.

At a crime scene, you'll encounter a variety of bugs, but certain ones tend to appear when there's dead flesh involved. To find out more about the significance of flies and beetles, check out the next page.

Forensic Entomology Techniques - Blow Flies and Beetles

Various types of bugs are attracted to a decomposing body, but the most common ones are flies and beetles. Flies, especially blow flies, can detect dead flesh within minutes. Fly larvae, known as maggots, do most of the consumption and contribute heavily to the decomposition of the body. Beetles typically arrive once the corpse begins to dry out.

When collecting insect samples, investigators aim to find the largest specimens, as the oldest insects will provide the most accurate PMI (postmortem interval). To preserve the insects, samples taken from the body are placed in containers filled with about 70 percent isopropyl alcohol, similar to the rubbing alcohol you can purchase in stores. These containers are labeled with the date, time of collection, and the body part from which the insects were taken. The investigator then either hands the specimens over to a specialist or mails them for further analysis.

In an ideal scenario, insects can provide a straightforward method for solving the unknown. For example, if someone dies of natural causes in a room with a constant temperature, and the coroner wants to determine the time of death, the entomologist can simply examine the insects found near the body and report the findings.

However, it’s rarely this simple. Investigators must account for several factors when collecting insect samples. The temperature surrounding the body, for instance, affects the speed at which larvae develop. If a person is murdered during the summer and left outside for several days, the temperature can fluctuate dramatically. Blow flies, for example, develop faster in warm weather but slow down when it’s cooler. Bodies left outdoors for weeks or months show significant variations in insect growth cycles, and the entomologist must carefully analyze the specimens to estimate a likely timeframe.

For further insights into how to catch the criminals, check out the next page.