Why Don’t Bugs Eat People’s Bones?

In her new book, Will My Cat Eat My Eyeballs: Big Questions from Tiny Mortals About Death, mortician and best-selling author Caitlin Doughty answers real questions she's received from kids about death, dead bodies, and decomposition. In the following excerpt, she describes why the creatures that consider skin and organs a tasty snack just don't feel the same way about our skeletons. (It's nothing personal.)

It’s a lovely summer day and you’re having lunch in the park. You bite into a fried chicken wing, munching on the crispy skin and juicy flesh. Is your next move cracking into the bones, crunching them like the giant in “Jack and the Beanstalk”? Probably not.

If you yourself wouldn’t eat a pile of animal bones, why would you expect a beetle to show up and eat your bones? We expect too much from necrophages, the unsung heroes of the natural world. They are the death eaters, the organisms that fuel up by consuming dead and rotting things—and bless their hearts! Imagine, for a moment, what the world would look like without the assistance of the consumers of dead flesh. Corpses and carcasses everywhere. That road kill? It’s not going anywhere without the help of necrophages.

Necrophages do such a good job getting rid of dead things that we expect them to perform miracles. It’s like how if you do too good a job of cleaning your room, then your mom will expect perfection every time. Better to not set expectations so high. It’s just not worth the risk.

The corpse-nosher ranks are filled with diverse species. You have vultures, swooping down for a roadside snack. You have blowflies, which can smell death from up to 10 miles away. You have carrion beetles, which devour dried muscle. A dead human body is a wonderland of ecological niches, offering a wide range of homes and snacks for those inclined to eat. There are plenty of seats at death’s dinner table.

Remember the dermestid beetle? The helpful cuties we’d enlist to clean your parents’ skulls? Their job is to eat all the flesh off without damaging the bone. Let’s be clear: we don’t want them to eat the bone. Especially because other methods of flesh removal (like harsh chemicals) will not only hurt the bones, but might damage certain types of evidence, like marks on bones, which could be useful in criminal investigations. That’s why you bring in a colony of thousands of dermestids to do the dirty work. Plus, while you were over here complaining that they don’t eat enough bones, the beetles were also eating skin, hair, and feathers!

All right, but to your question: why don’t they eat bones, too? The simple answer is that eating bones is hard work. Not only that, but bones are not nutritionally useful to insects. Bones are mostly made of calcium, something insects just don’t need a lot of. Since they don’t need much calcium, insects like dermestids haven’t evolved to consume it or desire it. They’re about as interested in eating bones as you are.

But, here’s a dramatic twist: just because these beetles don’t usually eat bone doesn’t mean they won’t. It’s a cost-reward thing. Bones are a frustrating meal, but a meal is a meal. Peter Coffey, an agriculture educator at the University of Maryland, told me how he learned this firsthand when he used Dermestes maculatus to clean the skeleton of a stillborn lamb. Adult sheep bones are robust, “but in fetuses and newborns there are several places where fusion is not yet complete.” When he removed the lamb bones after the beetles finished cleaning them, “I noticed small round holes, about the diameter of a large larva.” It turns out beetles will go after less dense, delicate bones (like those of the stillborn lamb), but, Peter says, “there has to be a perfect storm of good environmental conditions and poor food availability before they’ll resort to bone, which would explain why it’s not more commonly observed.”

So, while dermestids and other flesh-eating bugs do not usually eat bone, if they get hungry enough, they will. Humans behave the same way. When Paris was under siege in the late 16th century, the city was starving. When people inside the city ran out of cats and dogs and rats to eat, they began disinterring bodies from the mass graves in the cemetery. They took the bones and ground them into flour to make what became known as Madame de Montpensier’s bread. Bone appetit! (Actually, maybe don’t bone appetit, as many who ate the bone bread died themselves.)

It seems like no creature out there wants to eat bone, really prefers bone. But wait, I haven’t introduced you to Osedax, or the bone worm. (I mean, it’s right there in the name, people. Osedax means “bone eater” or “bone devourer” in Latin.) Bone worms start as tiny larvae, floating out in the vast blackness of the deep ocean. Suddenly, emerging from the void above is a big ol’ dead creature, like a whale or an elephant seal. The bone worm attaches, and the feast begins. To be fair, even Osedax don’t really devour the minerals in the bone. Instead, they burrow into the bone searching for collagen and lipids to eat. After the whale is gone, the worms die, but not before they release enough larvae to travel the currents waiting for another carcass to comes along.

Bone worms aren’t picky. You could throw a cow, or your dad (don’t do that), overboard and they’d eat those bones, too. There is strong evidence that bone worms have been eating giant marine reptiles since the time of the dinosaurs. That means the whale eaters are older than whales themselves. Osedax are nature’s peak bone eaters, and they’re even sorta nice to look at, orangey-red floating tubes covering bones like a deep-sea shag carpet. Pretty amazing, given that scientist didn’t even know these creatures existed until 2002. Who knows what else is out there in the world, devouring bone?

Reprinted from Will My Cat Eat My Eyeballs: Big Questions from Tiny Mortals About Death by Caitlin Doughty. Text copyright (c) 2019 by Caitlin Doughty. Used with permission of the publisher, W. W. Norton & Company, Inc. All rights reserved.