Why Don’t Insects Consume Human Bones?

In her latest book, Will My Cat Eat My Eyeballs: Big Questions from Tiny Mortals About Death, mortician and best-selling author Caitlin Doughty responds to actual questions posed by children about death, deceased bodies, and decomposition. In this excerpt, she explains why the creatures that often feast on our skin and organs aren't particularly interested in our bones. (It's not a personal issue.)

Imagine it’s a beautiful summer day, and you’re enjoying lunch in the park. You take a bite of a crispy fried chicken wing, savoring the skin and tender meat. Do you move on to crack the bones open, gnawing them like the giant from 'Jack and the Beanstalk'? Most likely, no.

If you wouldn’t gnaw through a pile of animal bones, why would you expect a beetle to come and munch on your bones? We often place unrealistic expectations on necrophages, the unnoticed yet vital creatures of nature. These 'death eaters' sustain themselves by consuming the decaying remains of the dead—and we should be thankful for them! Just think of a world without these decomposers. There would be rotting corpses everywhere. Roadkill? It’s not going anywhere without necrophages.

Necrophages do such an excellent job clearing away the dead that we begin to expect them to work miracles. It’s like when you clean your room so well that your mom starts expecting perfection every time. It’s better not to set the bar too high—it’s just not worth the potential letdown.

The ranks of corpse-eaters are filled with a variety of creatures. Vultures swoop down for a roadside snack, while blowflies can detect death from as far as 10 miles away. Carrion beetles feast on dried muscle. A dead human body becomes a buffet of ecological opportunities, offering homes and meals to those drawn to consume. There are always plenty of spots at death’s banquet.

Remember the dermestid beetle? The helpful little creatures we'd use to clean your parents’ skulls? Their task is to strip the flesh off without damaging the bone. Let’s be clear: we don’t want them to eat the bones. Other methods of flesh removal, such as harsh chemicals, can harm the bones and potentially destroy valuable evidence, like markings that could aid in criminal investigations. That’s why you bring in a colony of thousands of dermestids to do the job. And while you were complaining that they don’t consume enough bones, the beetles were busy munching on skin, hair, and feathers!

So, to answer your question: why don’t they eat bones too? The simple reason is that bones are tough to consume. Not to mention, bones offer little nutritional value for insects. They are primarily made of calcium, a substance insects don’t require much of. Since they don’t need calcium in large amounts, insects like dermestids have neither evolved to seek it out nor developed a taste for it. They’re about as interested in eating bones as you are.

But here’s a twist: just because these beetles typically avoid bones doesn’t mean they won’t nibble on them. It’s a matter of cost versus reward. Bones are a challenging meal, but when food is scarce, a meal is a meal. Peter Coffey, an agricultural educator at the University of Maryland, shared how he discovered this firsthand while using Dermestes maculatus to clean the skeleton of a stillborn lamb. Adult sheep bones are tough, but with fetuses and newborns, there are areas where the bones haven't fused fully. When Coffey examined the lamb’s cleaned bones, he noticed small round holes, about the size of a large larva. It turns out beetles will eat delicate bones (like those of a stillborn lamb), but Peter explains that it requires ideal environmental conditions and limited food availability before they resort to bones. This helps explain why it’s such a rare occurrence.

While dermestid beetles and other flesh-eating insects typically don't go for bones, they'll make an exception if they’re desperate enough. Humans are no different. During the late 16th century siege of Paris, when the city was starving, people resorted to digging up bodies from mass graves. They ground the bones into flour to create what became known as Madame de Montpensier’s bread. Bon appétit! (Though, in all fairness, maybe skip the 'bone appétit,' as many who consumed the bone bread ended up dying themselves.)

It seems no creature really craves bone, at least not in the way you might expect. But hold on, let me introduce you to Osedax, the bone worm. (The name kind of gives it away, doesn’t it? Osedax means 'bone eater' or 'bone devourer' in Latin.) These tiny larvae start in the deep ocean, awaiting their next meal. When a large dead creature, like a whale or an elephant seal, drifts by, the bone worms latch on and begin their feast. However, even Osedax isn’t really after the bone's minerals. Instead, they burrow in, searching for collagen and lipids to feed on. After the whale is consumed, the worms perish, but not before releasing enough larvae to drift with the currents, ready for the next carcass to appear.

Bone worms are not picky eaters. You could toss a cow—or, please don't do this—your dad overboard, and they'd feast on those bones too. There’s compelling evidence that these bone worms have been consuming giant marine reptiles since the time of the dinosaurs. In fact, these bone-eating creatures are older than whales themselves. Osedax are nature’s ultimate bone connoisseurs, and they’re even quite striking to look at. Their orangey-red, tube-like bodies cover bones, much like a deep-sea shag carpet. It's pretty mind-blowing, especially when you consider that scientists didn’t even discover these creatures until 2002. Who knows what other bone-consuming creatures are out there, waiting to be discovered?

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 from the publisher, W. W. Norton & Company, Inc. All rights reserved.