What do bugs have to do with forensic science?

A crime scene officer gathers evidence after a shoot-out in the Philippine financial district of Makati. She may not enjoy the smell, but surrounding insects would flock to it. What do creepy, crawly bugs have to do with investigations?
Luis Liwanag/AFP/Getty Images

As the old saying from the "Book of Common Prayers" goes, "Ashes to ashes, dust to dust." ­Sometimes recited at funerals, the phrase describes the cycle of life and how humans go from birth to death, from growth to decay. Forensic scientists and criminal investigators, however, should have their own version of the quote, something along the lines of: "Ashes to ashes, dust to bug food."

­When investigators attempt to solve a mysterious event involving sudden and unexpected death, they have to look at clues in order to piece together the events. They need to answer a lot of questions: What happened here? Who committed this crime? Why? What method, weapons or tools did they use? When did this happen? Using a vast background of science, including biology, chemistry, physics, anthropology and­ math, trained specialists can look at the fragments of evidence left over from a crime and, with care and precision, construct a legitimate story. They can use anything left at the crime scene, including broken glass, dirt, bodily fluids and any other trace elements.


Indeed, if we think of a crime scene, we usually envision yellow police tape, white chalk lines, broken glass and blood stains. But one item on or around a victim's body that gets a lot of attention during an investigation is actually a living organism, and it usually comes after a crime is committed -- the presence of insects. 

­What can bugs tell us about death? How much can they reveal about a crime? And can forensic entomology help with anything other than legal cases involving death? To learn how bugs help us fight crime while finding time for a tasty snack, read the next page.

Forensic Entomology - Bugs and Bodies Go Together

Several of Arthur Conan Doyle's Sherlock Holmes stories refer to dead bodies covered in insects.
Time Life Pictures/Mansell/Getty Images

Just as flies will flock to a piece of rotting meat left out on the table, necrop­hilous insects, or dead flesh-eating bugs, are often associated with human corpses. Forensic entomology, or the use of insect evidence in both criminal and civil cases, helps police and criminal investigators learn a great deal about what happened to a body.

­The major criminal field of forensic entomology is known as medicolegal entomology. It's also known as forensic medical entomology or medicocriminal entomology because of its focus on violent crime. People working in this field usually attempt to determine several important things:


  • The PMI (postmortem interval), or the estimated time of human death
  • The location of death
  • Legal cases involving mysterious, sudden death where foul play is suspected
  • Traffic accidents with no apparent cause
  • Criminal misuse of insects

Bugs found in the orifices of a deceased human body, such as the eyes, nose, ears and mouth, will arrive very quickly. Most insects can locate the smell of dead flesh within a matter of hours after expiration, and some insects, known as carrion insects, live their entire lives feeding on dead flesh and developing more generations of bugs. Adult carrion insects, mature and capable of movement, will fly to the nearest dead body to lay their eggs inside.

­Indeed, the fact that bugs will develop and grow inside a corpse is one of the most important aspects an entomologist keeps in mind when investigating a death. There are generally three stages an insect goes through during its lifetime inside a dead body. The first stage is the egg stage, where the insects are still enclosed within their eggs; the second stage is the larva stage, where the small, white larvae that have just emerged from their eggs grow by feeding upon the dead flesh; and the final stage is the pupa stage, which is an intermediate stage that comes before the insect turns into a winged adult. ­

If an entomologist collects insects from a corpse during any one of these stages -- egg, larva or pupa -- and understands the life cycle of that type of insect, he can determine a fairly accurate time of death. In other words, the entomologist needs to understand two basic facts: how long after death the insect eggs are laid plus the amount of time it takes for the insects to develop. These two facts should give him a good idea of how long a person has been dead.


­ You'll find all kinds of bugs at a crime scene, but there are a few that typically show up for a dead flesh party. To learn about the importance of flies and beetles, read the next page.

Forensic Entomology Techniques - Blow Flies and Beetles

A large, adult blow fly, who must have received his fill of human remains.
Bruce Marlin

Many kinds of bugs will flock to a decomposing body, but the most common kinds of bugs found on a corpse are flies and beetles. Flies, particularly blow flies, can find dead flesh within minutes. Fly larvae, commonly known as maggots, do the majority of the eating and are responsible for much of a corpse's decay. Beetles, on the other hand, will typically move in once a corpse has dried out.

When collecting insects, investigators try to locate the largest specimens -- the oldest bugs should give the best PMI (postmortem interval). To preserve the insects, samples taken from the body are placed into containers filled with about 70 percent isopropyl alcohol, the same strength as the rubbing alcohol solution you can buy at the store. The containers are labeled with the date and time of the collection and the part of the body from which the insects were taken. Finally, the investigator either delivers the specimens directly to a specialist or mails the containers expressly for examination.


Forensic entomologist Neal Haskell speaks to the jury about insect activity used to date the time of death of 11-year-old Carlie Brucia.
Chip Litherland-Pool/Getty Images

In a perfect situation, insects can prove an easy tool for uncovering the unknown. For instance, if a person dies of natural causes in a room where the temperature has remained constant and the coroner wants to know the time of death, the entomologist simply looks at the bugs around the corpse and reports the details.

It's almost never that easy, however. Investigators need to take into account a large number of variables when collecting specimens. The temperature of the surrounding area, for example, determines how quickly larvae will grow in a corpse. When a person is murdered during the summer months and left outside for several days, the ambient temperature surrounding the corpse can change dramatically. Certain types of blow flies develop faster during hot weather but development slows down when it's cooler. Bugs found on a body that's been outside for weeks or even months show drastic variations in growth cycles, and an entomologist needs to carefully observe the available specimens to determine a likely range.


­ For lots more information on how to catch the bad guys, see the next page.

Lots More Information

Related HowStuffWorks Articles
More Great Links


  • Bullington, Stephen. "Forensic entomology." Forensic Entomology. http://www.forensic-ent.com/
  • Hall, Robert. "American Board of Forensic Entomology." University of Missouri. http://research.missouri.edu/entomology/
  • Tomberlin, Jeffery, John Wallace and Jason Bird. "Forensic entomology: myths busted!" Forensic Magazine. Oct. and Nov. 2006. http://www.forensicmag.com/articles.asp?pid=112