30 Nov 2012

A Tribute to Scavengers and Decomposers

by Jan Thornhill

I visited a school a few days ago to talk about my books and, as usual, passed around the contents of my “museum-in-a-bag,” a collection of, among other things, skulls, dinosaur bones, desiccated insects, snake skins, feathers, and a mummified bat and two hummingbirds. The children are always very careful with my treasures, but that day my white-tailed deer skull finally snapped in half. I wasn’t exactly surprised, since this particular skull has been handled by at least 5,000 kids over the past few years. Besides, I can always glue it back together again. I’d like to save it, though, because, like many of the things in my bag, the deer skull has a story.
White-tailed deer skeleton (Jan Thornhill)

I found it, along with most of the rest of the deer’s skeleton behind a fence on my road. It’s not hard to imagine how the animal died: I’m sure someone struck it by accident with their car. Though mortally injured, it must have managed to make two great bounds, one to get off the road and the other to get over the fence. The person who hit it must have been relieved to see it disappear into the brush as he or she drove away. But then, alone, the deer collapsed and died.
A year earlier, I had looked for puffballs in exactly the same spot in late autumn. There were no deer remains then, so the longest it could have been hidden there was twelve months. Amazingly, other than a few wisps of hair and a couple of snippets of dried skin, the skeleton was completely clean – clean enough that I had no qualms about bringing it home.

So who do I have to thank for cleaning those bones for me? Scavengers and decomposers, that’s who – my favorite characters in the food chain.
I was quite sure a coyote must have visited the corpse of the deer shortly after it died since the bones of two of its legs were missing. The coyote is the only animal in my neighborhood that is strong enough to drag away such large parts. Though they’re predators, and often hunt for food, coyotes are also such frequent scavengers that they’ve developed a special receptor in their brains that makes them immediately throw up anything that is dangerously rotten. So a coyote wouldn’t have had to feed on the carcass immediately, especially if the deer had died in the cold of winter.
Coyote feeding on elk carcass (Courtesy Bryan Harry, U.S. Fish & Wildlife Service)
Turkey vulture
Other scavenging mammals, such as foxes and skunks, might also have visited the corpse, as well as birds, such as crows and vultures. Our local turkey vulture is one of the few large animals that is a dedicated scavenger, which means that its only food is carrion, or already dead or decaying flesh. They’re perfect for this job: they have an extremely well-developed sense of smell that allows them to home in on food that's miles away; their bald heads reduce the amount of rotting matter that might stick to them; strong acids in their digestive tracts destroy harmful bacteria; and their urine is also very acidic – and here’s the best part – so they pee down their legs to let the acid destroy nasty bacteria clinging to them. 
As well as being fed upon by these larger animals, in the warmer months corpses attract an amazing number of insects. A variety of flies are lured by the smell of death and lay their eggs. Their larvae, or maggots, are voracious carrion feeders. Flesh-eating beetle larvae continue the job and, later, other beetles with specialized mouth parts show up to feast on tough skin and ligaments, followed by moths that eat fur and hair. These insects all arrive at such specific stages of decomposition that forensic entomologists, scientists who study the insects that are found on or near dead things, can use their knowledge of this progression to determine the time of death when the remains of a human are found.
Close-up of a blowfly maggot (Eye of Science)
Throughout this whole process bacteria are active, gobbling up the corpse from within. These bacteria produce gases as a waste product, and it’s these gases that are responsible for the putrid odors that waft off rotting animals. Humans are naturally revolted by these smells, which is a good thing. If we weren’t disgusted by the smell of decomposition, we might be tempted to eat food that has gone bad and get sick from the bacteria growing on it. Interestingly, almost everyone in the world says the same thing when confronted by these smells, some version of “Yuck!” or “Ick!” This verbal gagging is so natural and so universal that some people think it might be the way that human language began.
My tip to anyone who finds an animal skull (or other bones) and wants to bring it home, is to use your eyes and nose. If it looks gross and smells disgusting, leave it where it is. Mark the location and return in a few months. More often than not, scavengers and decomposers will have completely cleaned it up for you.

You can find out lots more about death and decomposition in my book: I Found a Dead Bird: The Kids’ Guide to the Cycle of Life & Death (Maple Tree Press)
Here’s a fun, time-lapse video showing a watermelon decomposing over 35 days: http://thekidshouldseethis.com/post/12926682492

1 comment:

Leslie Lim said...

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