Like it or not, bugs aren’t going anywhere—and it’s clear that they continue to both horrify and fascinate us.
Our story last week squashed some of the more persistent bug myths, but it also generated many more urban legends and questions suggested by our readers. So we just had to do a follow-up.
Here’s what the experts had to say about giant killer bugs, pesky fleas, and beetles that supposedly devour human flesh.
In the movie The Mummy, scarab beetles attack people, crawling under their skin and eating them alive. Can scarab beetles actually do this?
“The word ‘scarab‘ is used to describe any member of the beetle family Scarabaeidae,” May Berenbaum, an entomologist at the University of Illinois at Urbana-Champaign, said in an email. But it’s also used to refer to the Egyptian scarab beetle, Scarabaeus sacer, which is a kind of dung beetle, she says.
Egyptian scarab beetles “are anatomically equipped for moving in and around excrement and digging into the ground to bury [their] dung balls,” Berenbaum says. “They’d have a hard time penetrating skin and then maneuvering through flesh.”
But there is a medical condition known as either canthariasis or scarabiasis, which describes a rare, temporary infestation of a person’s gut or face with beetle adults or larvae. A 2008 report in the journal Indian Pediatrics described such a case in a four-year-old girl from a village in India.
The beetles could enter a human body through the anus while in search of food, Berenbaum notes.
Most people don’t have to worry about this, though: “Generally, this condition is restricted to places where basic hygiene practices are ignored or abandoned,” says Berenbaum.
Can fleas live on a human body, and if so, for how long?
“In the United States, we do not have flea species that reside on people,” says Michael Dryden, a veterinarian professor who studies fleas at Kansas State University. There is a group of fleas in the genus Pulex that can call primates—including us—home. But they are fairly rare in industrialized nations such as the U.S., he explains.
During Europe’s Middle Ages and America’s colonial days, those fleas were much more common on people. Now, when they do pop up in the U.S., they are found on animals like opossums, Dryden says.
Today, the flea species many of us are concerned about is Ctenocephalides felis, commonly found on cats and dogs, he adds. (See “How Do Fleas Jump? New Video Solves Mystery.”)
“That flea will feed on us,” Dryden explains. The females need a blood meal in order to produce eggs, much like mosquitoes do. But they don’t call people home or lay eggs on us the way they do on cats, dogs, mountain lions, or opossums, he says.
No one knows why C. felis won’t live on people, Dryden says. “There are over 2,200 species of fleas worldwide,” the researcher says, with “over 400 species of fleas in North America.” Some are quite picky and will live only on a particular host, while others “are more cosmopolitan in their tastes.”
Is it true that when you squash a cockroach, you release their eggs? Would you then spread the eggs when you walked?
“No,” says Roberto Pereira, an entomologist at the University of Florida in Gainesville. Cockroaches bundle their eggs in a hard brown casing called an ootheca, which they will then glue to surfaces including furniture.
Some species, like the German cockroach, will carry their ootheca on their abdomen until the eggs hatch. Madagascar hissing cockroaches will hatch their eggs inside their body and then release their young.
In any case, if you step on a cockroach, “you’ll very likely kill everything,” Pereira says, including any eggs or young ones. (See “Cockroaches Have Neighborhoods, Too.”)
Could a nuclear blast or radiation leak produce giant killer insects?
“No,” says Dan Babbitt, manager of the insect zoo and butterfly pavilion at the Smithsonian’s National Museum of Natural History in Washington, D.C. There’s a limit to how large insects can get, thanks to how they breathe.
Since they don’t have lungs, they breathe through tiny tubes that run from the surface of their body down to their cells. It’s a passive connection that relies on a specific concentration of oxygen in the atmosphere, Babbitt explains.
With the amount of oxygen swirling in our atmosphere today, you wouldn’t be able to get a giant insect like you see in B-list horror movies.
During the Carboniferous period 359 to 299 million years ago, however, there was a lot more oxygen in Earth’s atmosphere than there is now, Babbitt says. And so that period of Earth’s history supported insects that were much larger than the ones today.
There were dragonflies with 12-inch (30-centimeter) wingspans and “spiders the size of a garbage-can lid,” Babbitt explains.
Can spiders really lay their eggs in a person’s skin?A brown recluse spider. Its bite can result in nasty, necrotic wounds. Photograph by Alex Wild, Visuals Unlimited/Corbis
“It’s very unlikely,” says the University of Illinois’s Berenbaum. The structure they use to lay their eggs, called an ovipositor, isn’t really built to do any injecting, she explains.
“I suppose a spider could drop or plaster eggs on the skin’s surface,” Berenbaum says, “but it’s not clear why a spider would want to do such a thing.” (See National Geographic pictures of beautiful insect eggs.)
The Smithsonian’s Babbitt adds that spiders usually wrap their eggs in silk, forming a little sac or ball. And they generally leave those sacs on a web or in a covered area like under a stone. “But never on an animal as far as I know,” he says.
Is it true that cockroaches can’t crawl backward? If they crawl into an ear, would they be able to make it back out?
“A lot of insects are not great at moving backward,” says Babbitt. That’s partly due to the fact that many of them have spines on their legs that make it difficult to back out of a narrow passage, he explains.
The University of Florida’s Pereira decided to test whether a German cockroach could back out of a narrow, clear plastic tube. It did in fact wriggle backward, he says, trying to get itself out of the tube.
So it’s not unreasonable to think that “given a chance, [a cockroach] would back out of an ear,” Pereira says.
Are there instances of insects preserved in amber being infested with twisted-wing parasites?
This isn’t strictly a myth or urban legend, but the thought of insect parasites being entombed with their victims for millennia is intriguing.
Modern twisted-wing parasitoids, also known as strepsipterans, are parasites that live inside a group of insects including bees, wasps, and grasshoppers.
Young twisted-wing parasitoids burrow their way into a suitable insect or spider host and feed off of it until they can emerge as adults. (Also see “‘Vampire’ Parasite Found Entombed in Amber.”)
There are, in fact, several lineages of strepsipterans found in amber, says Conrad Labandeira, curator of fossil arthropods at the National Museum of Natural History. The oldest such specimens go back to the Eocene period, between 37 and 56 million years ago.
Researchers have found both male and female adults locked in amber, Labandeira says. But he can’t recall an instance where an insect host and the twisted-wing parasitoid were both found in the same piece of amber.
There are instances where host insects trapped in amber have nematodes—parasitoids that look like skinny worms—with them. (See “Photo: Mite Attacking Ant Entombed in Amber, Oldest Fossil of Its Kind.”)
The parasitoids are frozen in the act of crawling out of the host. “You can see the nematodes trying to escape into the amber,” Labandeira says.
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