Crime scenes, especially those involving a deceased victim or victims, are amazingly complex. Recovering evidence and understanding its significance in detailing the interaction between the victim and assailant can be very challenging and can be made even more so when animals interact with the evidence.

Animals can damage or completely destroy evidence. Further, such damage can be difficult to distinguish from human-inflicted wounds and lead to false conclusions. So studying and analyzing the effects of animal-cadaver interaction can shed light on cause of death, original position of the body, and time since death. 

But how animals affect remains at crime scenes is not just a subject for scientific study. It is a real-world concern. Consequently, it is important for all officers, from the newest first responder to the most seasoned investigator, to be familiar with the impact animals can have on crime scenes.

Insect Effects

Insect infestation of the cadaver usually occurs at putrefaction. Chiefly, insects around a human cadaver fall into four categories: those feeding on the cadaver; those feeding on the insects eating the cadaver; those feeding on all of the above; and those using the cadaver as a living environment. Blow flies and beetles are the most common insects to feed on a cadaver. Wasps and ants may feed on either the cadaver or other insects, while spiders do not consume the cadaver but rather use it as a living environment. Forensic entomologists research the many waves of insect activity around a cadaver, which can vary greatly by environment.

There are different, yet sometimes overlapping, sets of insects that affect a cadaver depending on where it is located. Bodies that are buried are not affected by surface insects and bodies in water are affected more by fish than by insects, unless some portion is exposed above the water's surface. Other external factors such as geography, temperature, humidity, presence of sunlight, season, resource competition, and manner of death all control what types of insects are present. For example, maggots cannot tolerate sunlight. Often, they eat everything except the outer skin of a cadaver. In most domiciles, blow flies and other insects are not present.

The growth stages of several insects that feed on cadavers is well known, allowing scientists to formulate a rough time of deposition or death based on the life stage of the insects present. Maggots are particularly helpful in toxicological examinations as they retain any poisonous substances present in the tissue they consumed. Large maggots in particular are good for such toxicological exams.

Insect activity can also show the location of soft tissue wounds long after the tissue has decomposed. A concentration of maggots in one area of a corpse usually signifies the presence of a wound, as the maggots feed on blood and tissues, usually beginning at a natural body opening or artificial defect such as a stab wound or gunshot wound. This inference may be the only clue remaining that a crime had been committed.

Concentrations of maggots are also helpful in discovering the original location of a body. The cadaver, either moved by animal or human, often seeps body fluids that collect in the ground and attract insects. A high concentration of insects on some odorous earth often signifies that a body was in that spot.

Although common house flies may lay eggs in body orifices like the eyes, nose, and mouth, most indoor insect activity can be attributed to the cockroach and this activity can lead to issues with the evidence.

Cockroaches have been known to begin feeding on people who are not yet dead, but mostly immobile. Roach bites are small and reddish, usually occurring around facial orifices, and the bites can be mistaken for antemortem physical abuse when they occur on children since the damaged areas may be quite large. A large affected area, teamed with the fact that the bites look like abrasions, can lead to false conclusions.

Other insect bites, like those of the ant, can be confused for perimortem trauma, with some sources noting the similarity between ant bites and other types of trauma. In one case, such bites were identified as fingernail marks left by a rapist until microscopic examination proved otherwise. The feeding marks of shrimps and crabs, like roaches, share a resemblance to some types of abrasive trauma. To differentiate between insect and crustacean damage and abrasions, one must look for bruising associated with physical trauma.

Birds Feeding

It tends to be a trope in most Hollywood films that birds are the chief scavengers of human cadavers. Numerous movies show birds pecking out eyes and tearing off snips of flesh from human bodies. This can be both accurate and inaccurate, depending on the birds involved.

It is absolutely true that birds are usually present at most outdoor cadaver sites, but many tend to be preying on insects that are consuming the body and not the body itself. Of course, as everyone who has ever seen roadkill knows, some species like vultures and buzzards do feed on carrion, including human cadavers, sometimes in a specialized manner. One study noted a buzzard makes a surgical strike to the gut of the cadaver to remove the intestines, leaving the other organs untouched.

Dogs and Cats

Much non-insect cadaver scavenging is done by dogs, cats, and rodents. More on rodents in a minute; for now let's discuss dogs and cats.

In the wild, wolves, coyotes, and mountain lions are the key species that tend to prowl around North American crime scenes and body dumps. In urban environments pet dogs and cats can be primary scavengers of human remains.

Significant damage can be caused to human remains by dogs and cats, both wild and domesticated. Destruction and scattering of body parts; alteration or complete destruction of bodily evidence related to cause of death; and creation of new artifacts on soft tissues, bones, and other body surfaces are just some of the major effects of dog and cat activity.

Animals large enough to move the cadaver can greatly change the appearance of the scene. A case from California highlighted this when a mountain lion attacked and dragged a woman. While being dragged, the woman's bra and shorts were moved and appeared to evidence a possible sexual assault. With additional evidence and expert consultation, the scene was recognized for what it was, a mauling by a predatory cat.

Canines such as dogs and coyotes, especially if working as a pack, can cause significant damage to a cadaver, including removal of limbs and complete disarticulation of the body. But there are many factors that affect how much damage dogs can do. For example, the build of the person along with any surrounding garments or materials may restrict the dogs' access to joints and connective tissue, limiting the severity of destruction.

While dog damage to a cadaver can be devastating and literally tear a cadaver apart, it is mostly in the form of tooth marks on bone. These gnaw marks fall into four distinct groups: punctures, pits, scoring, and furrows. Punctures pierce bone, whereas pits merely dent it. Scoring is a slip of the teeth on bone and furrows are usually seen as unidirectional grooves. Soft tissue may also preserve, for a time, the V-shaped piercings of the canid canines. Of note, human biting, conducted as part of a crime, may be evidenced on the body and mistaken for animal activity.

Rats

Most animal activity in an urban setting is conducted by rodents. Rats and mice with their chisel teeth and exploratory behavior often feed on newly deceased persons, usually starting on the unprotected face and neck. The damage they inflict tends to be less extreme than that of a cat or dog, but telltale grooves left by their chisel teeth can usually be seen in the flesh or bone.

Apex Predators

Human beings are the world's greatest predators, but this planet is also occupied by a variety of animals capable, alone, of attacking and eating a live human being. Bears, big cats, sharks, and crocodilians are examples of what zoologists call apex predators, meaning they reside at the top of the natural foodchain and are only prey to humans. These animals account for an unknown number of human deaths per year and they commonly eat human remains of both people they kill and bodies they scavenge.

Bears, as shown in the recent movie "The Revenant," can and will attack humans, and they are known to scavenge on human remains in the woods and forests of North America. Big cats are generally more of a problem in Africa and Asia, but mountain lions and other types of American panthers are found in the United States, even on the outskirts of urban areas like Los Angeles and Phoenix. Panthers are even being sighted once again in South Florida.

Sharks are mythically famous for eating humans, despite the rarity of actual documented attacks. Movies, TV, and books have perpetuated fear of these ancient fish. This fear, it must be admitted, is grounded in some truth. Sharks are sometimes caught by fishermen who later find human remains in the stomach and digestive tract.

Often victim identification is impossible unless the body part has some identifying mark like a tattoo, very unique scar, or medical implant with a serial number. Sharks digest food slowly and sometimes selectively. It is known that a shark can hold human flesh in its stomach for 8 to 21 days. Forensically, sharks can be important when they ingest disposed human remains, although recovering evidence from a shark is difficult, as is differentiating between humans killed and simply scavenged.

Similar issues arise when dealing with alligators and crocodiles. Both are opportunistic feeders and will readily consume a cadaver or any portion thereof. This is why some criminals favor Southern swamps for disposing of bodies. Alligators and crocodiles eat food in torn chunks, thus the remains of humans are often found in pieces.

Animal activity in relation to forensic investigations is a major concern. Investigators must be trained to recognize animal and insect scavenging and be able to distinguish these post-mortem traumas from perimortem traumas. Failing to have the proper training and expertise can lead to false conclusions about the scene and if a crime was actually committed. Further, the activity of animals like insects and canids can give investigators valuable clues that might have otherwise been lost as the body decomposed.

Don Arp Jr., has a masters of arts in anthropology and a B.A. and a certificate in forensic science from North Central State College in Mansfield, OH. Arp is widely published, with his work appearing in the FBI Law Enforcement Bulletin, IAI Nebraska Chapter Newsletter, and the Journal of Forensic Identification. His work on effective police reports is cited in three textbooks: "Criminal Investigation," "Police Operations: Theory and Practice," and "Introduction to Private Security."