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The hole truth about animals that bore

July 9, 2015
Tanea undulata, a Moon snail from East Timor. Photo by Nick Hobgood. Licensed under CC BY-SA 3.0 via Wikimedia Commons.

Summer is here, it’s hot, the kids are out of school, and by now I expect they’re pretty bored. Perhaps it’s time to go outside and see how bored other things are. For instance, if you’re at the beach, you might find a clam shell with a perfectly circular hole in it. That’s a bored clam shell. Or maybe you’re lucky enough to find a rock or coral with some broad holes in it. Or maybe you notice holes in trees or logs. These are all bored, too.

But what causes all these objects to be so bored? In the case of the shell at the beach, the answer is predatory snails. Some snails – particularly moon snails – soften a clam’s shell by using a boring organ that produces hydrochloric acid, enzymes and other substances. Then the snail rasps the softened clam shell with a hard plate called a radula, resulting in a circular hole. If you look closely at it, you’ll see the hole is wider on the outside than on the inside of the shell. Once the snail breaks through the shell, the snail uses its radula to rasp away the clam’s soft tissues, basically eating the clam alive. Now that’s both boring and exciting!

Broad holes that you might find in rocks or coral are made by boring clams. (This means you can be as happy as a clam or as boring as a clam.) Certain clams, such as angel wings, piddocks or pholad clams, use the rough edges of their shells like files to slowly grind against rocks or corals, twisting themselves in. These clams rotate into rock at a rate of 4 or 5 centimeters (about 2 inches) per year, which is slower than your fingernails grow. Most boring clams stop when they’ve bored a hole the length of their bodies, but some drill themselves several body-lengths deep over the course of their lives. These clams eat by extending tubes called siphons (much like a vacuum-cleaner hose), to filter feed on passing plankton. But once they’ve lodged themselves in a coral or rock, they don’t leave. They’ve literally dug their own graves.

A clam that bored into a coral. This specimen is from the Museum's invertebrate paleontology collection.

A clam that bored into a coral. This specimen is from the Museum’s invertebrate paleontology collection.

Not only are some snails and clams boring, but certain insects are boring too. Got holes in your floor, wood siding or in the dead tree in your yard? These are likely the result of wood-boring beetles, termites, carpenter ants or carpenter bees. Even non-insect arthropods, such as some isopods (think “roly-poly pillbugs”), can bore into wood. Whatever animal is eating into your wood, you can bet it is boring.

So, let’s say I’m a paleontologist (which I am). I may not find remains of the actual animal that made holes in fossil shells or petrified wood. But by studying the shape of the hole, the bored substratum, and by knowing a little bit about different animals’ behaviors, I can deduce what animal might have been boring. Ichnology, the study of traces, can be a lot like forensic detective investigation. To me, that’s not boring, that’s fascinating.

Reprinted from The Charlotte Observer and Raleigh News & Observer

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