The Perfect Witness Can't Lie. But Can They Buzz?

Insects are everywhere in our lives: visiting our flowers, poking through our trash, or hiding out in our cupboards. Most would consider them disgusting, especially the flies and maggots that hang around rotten food. Rotten food, though, has a lot in common with rotting bodies, and flies aren't picky. Investigators of crime scenes can use these scavenging bugs, then, to tell the story that a victim can't. In the field of forensic entomology, insect evidence gives valuable clues about how and where a killing happened.

Forensic entomology as a field dates back as far as forensics itself. Collected Cases of Injustice Rectified, a book from 13th century China written by judge and scholar Song Ci, is the first ever book of forensic science, detailing how to identify causes of death and perform autopsies. It is also the first known application of forensic entomology. 

In 1235, Song Ci writes, a stabbing occurred in a Chinese village. The weapon of attack was determined to be a sickle after various sharp objects were tested against an animal corpse. All the villagers were ordered to place their sickles on the ground, but only one of them attracted blow flies, which were drawn to the remnants of blood, tissue, and hair left on it. The owner of the sickle confessed to the murder and was led away ashamed.

Blowflies on some dead stuff. It's hard to find pictures when you have a massive phobia of maggots. Ew ew ew.

After nearly 8 centuries, the field has become considerably more sophisticated. Insects collected from corpses can give valuable information about both the time and location of death, and even if drugs are present in the deceased's system. 

Time of death is the most easily approximated, using what we know about insect life cycles. First on the scene, and most valuable to investigators, are flies, usually blowflies or fleshflies. Attracted by the chemicals created by decomposition, these scavengers feed near orifices such as the mouth, or open wounds, blowflies colonizing the body within a few minutes of death. 

Later on, flies lay their eggs on the body, which hatch into maggots. By identifying the species and age of the maggots, investigators can find out how long ago they hatched, and approximate a time of death that way. Other insects come along during later stages of decomposition: beetles, mites, and moths. Entomological data can be incredibly accurate: before 24 hours, it is even more accurate than soft tissue analysis in determining time of death, and after 72 hours, insect evidence is sometimes the only method of determination.

One of the major concerns of forensic entomology is finding bibles small enough to swear in the witnesses.

The insects present can also tell where the death took place with surprising specificity. For example, if flies are on a corpse that aren't native to where it was found, this is good evidence that the body was moved after death. Insects in general also like warm, moist environments. If a body is left out in the sun, then, larvae will exhibit faster development, and be more numerous. The same is true if in a humid or rainy place, allowing investigators to pinpoint which areas are likely for a murder.

Even still, insects can be drug-tested for compounds present in the corpse when a toxicology report is impossible or needs more evidence, such as when soft tissues or bodily fluids have decayed. In the emerging field of entomotoxicology, investigators can test insects to find if substances are present in their tissue. Some substances also alter the time of development: generally, cocaine and methamphetamine cause faster growth, while some poisons, such as barbiturates, slow down development.

In an age where many forensic techniques are being proved unreliable or even pseudoscientific, new approaches to convicting killers must be based on hard evidence. Bite mark analysis, bullet lead comparison, and fingerprinting, all things we think are damning evidence, have actually been shown to be highly unreliable. Forensic entomology fortunately seems less "buggy", and as the field expands, we may see more flies and beetles convicting bad guys.