“The Worms Crawl In, the Worms Crawl Out…”
by Gretchen Noyes-Hull
The pungent odor of fermenting flesh has led you and the forensic detective to the decomposing body, thinly buried under dry leaves, but it's the roiling mass of maggots you see that releases the old children's song in your head: “The worms crawl in, the worms crawl out. . .” UGH! The sight of the seething hungry larvae is not a pretty one.
Although disgusting to most of us, the wriggling swarm captures the full attention of the forensic investigator, who quickly reaches for his forceps.
“Sick!” you scream, as you watch him plop specimens first into hot water and then into carefully labeled vials of alcohol.
“Gross!” you grimace, as he drops globs of the writhing white larvae onto tidbits of decaying meat in waiting collecting jars! It's enough to make your own skin crawl!
“The Worms Play Pinochle on My Snout…”
The tune continues in your head. As though there were time for play!
Long praised for their speedy recycling of cadavers, these morbid insects — the blowfly, flesh fly, “cheese skippers,” and beetles — keep the Earth from filling up with slowly decomposing corpses. Digging in with voracious appetites for decaying flesh, they can reduce a human form to a loose collection of bones in a matter of months!
Recently, these distinguished but diminutive bugs have earned recognition as expert witnesses in the courtroom. Frequently first to arrive at the scene of a crime, they often have the last word in front of a jury. Dead men don't talk, but the insects that feed on them sometimes do! And it is the job of the forensic entomologist (insect scientist) to find out what they say.
When someone happens upon a body, a forensic entomologist is often called on to pinpoint the time, place, and even cause of death. An entomologist studies insects and their interactions with their environment. Most forensic entomologists specialize in those insects that make their living on decomposing cadavers.
A victim's loss is their gain. To a great number of insects, the random appearance of a nutritious corpse is the opportunity for an entire lifetime and life cycle. The advantage of having a stationary meal is offset slightly by the uncertainty of not knowing where the next body might fall. But insects that depend on dead flesh have developed an uncanny ability to locate them. Within hours of death (and in some cases even sooner), the first ones arrive, attracted by the very first whiffs of putrefaction.
What's the Buzz?
Most people have never considered an infested corpse to be a complex ecosystem, but a forensic entomologist is keenly aware of the succession of creatures that move in on a cadaver from start to finish.
First arrivals include the blowflies searching for choice locations to lay their eggs. Open wounds are best, but if there are none, these eager insects first pack the openings of the face and then move down the corpse to find other entries. Flesh flies follow when conditions are just right, laying live larvae in locations where they can begin to feed.
As decomposition proceeds, the meal becomes appetizing to waves of other settlers. After a few months and the body's loss of fluids, conditions are ripe for the “cheese skippers” to begin nibbling on remaining protein, leaving only skin and bones for the beetle brigade that follows.
Cadaver larvae proceed through very definite stages to adulthood. The eyeless, legless fly maggots grow rapidly, shedding their skins several times. When the last maggot stage is reached, the larvae crawl to a drier location (hair, clothing, or the ground) and “pupate,” the last outside skin drying to serve as protection for the metamorphosis into the adult. Entomologists know from laboratory studies just how long each stage takes under different conditions of humidity and temperature.
But what does the entomologist do with the vials and sample jars? The hot water treatment prevents shrinkage of the bugs in the alcohol preservative, while the rotting meat in the collection jar provides an alternative menu for those lucky enough — for a while — to be kept as live samples.
From the preserved maggots, the forensic entomologist is able to identify and measure the length of the different stages and estimate how long they have been growing since the eggs were laid. Since the larvae of most of the fly species all look white and wiggly, some of them must be raised to adults before they can be properly identified. From the combined data, a time of death can be calculated — since insects generally wait for the victim to die before moving in.
The Evidence Is In!
When bugs are put on the witness stand, their testimony can affect even what is seemingly a cut-and-dried case. Little time has passed since the murder if blowfly eggs are still present, unhatched. Masses of maggots may signal wounds that were undetectable in the decay, revealing unsuspected violence as the cause of death. The different kinds of larvae present can even determine whether a body has been moved since death. If maggots from city-type flies are found on a corpse in the countryside, it can be concluded that the body has been transported. (There goes that alibi about being in the city at the time of the murder!) And what about the body with an infestation of shade-loving, indoor insects that is found in bright sunlight? The flies don't lie.
In courtroom appearances, then, few “witnesses” are better at “singing” than a forensic entomologist's friends. Speaking of which, now if you could just get that song out of your head!
The Rice Paddy Mystery
The earliest recorded use of insects to document a crime comes from the 13th-century China. A rice harvester was fatally stabbed with a sickle. The following day, an investigator asked all workers to bring their sickles and lay them on the floor. As everyone stood back and watched, flies settled on only one of the sickles, drawn there by the scent of blood. The owner confessed to the murder.
Insects can help solve drug cases, too! Packages of marijuana (Cannabis) may contain hideaway bugs that help to identify where the plants were grown. And since insects accumulate drugs in their bodies during feeding, they sometimes contain levels of opiates or barbituates that are no longer detectable in the corpse on which they were feeding.
- A dead body.
- The breaking down of plant or animal matter by bacteria or fungi.
- The decaying or rotting of something.
- Very small or tiny.
- All of the living and nonliving things that interact with one another in a given area.
- Decomposition of organic material by microorganisms, resulting in the production of foul-smelling matter.
- Consuming or eager to consume great amounts of food.
- How is a decomposing body part of a food web? Draw a food web that includes at least two food chains and the decomposing body of a mouse.
[anno: Students' drawings will vary, but should include a dead mouse as the food source for decomposers, such as blowfly larvae.]