National Geographic Tales of the Weird

by David Braun

  Researchers then removed egt from some viruses, reinfected the caterpillars, and found that the zombie behavior stopped. When the team inserted the gene into a virus that previously lacked it, the zombie behavior returned.

  “Somehow or other, using this gene, the virus is able to manipulate the behavior of the caterpillar to go to the right location in the tree to enhance transmission to new hosts. It’s really amazing,” Hoover said.

  The gene may work by deactivating its hosts’ molting hormone, according to the study, published in the journal Science. “That would be an advantage to the virus because it keeps the insect in a feeding state, so that they get bigger and bigger and make more and more virus.”

  Not Berry Funny

  In Central and South America, scientists have discovered a parasite that makes ants look like red berries, which tricks birds into eating them. The parasites travel through the birds intact and are then defecated out onto leaves. New ants eat the leaves and are exposed to the parasite, which allows it to keep spreading. As insect ecologist Steve Yanoviak explains it, “No matter how we look at it, somehow that parasite has to infect new colonies, or else it would die … So there has to be a mechanism for transport to a new colony.”

  Natural Enemies

  There are many different types of baculovirus, Hoover said, and almost all caterpillar species are infected by one or more of them. But the virus, which is naturally occurring, doesn’t greatly impact gypsy moths as a species, Hoover said. Gypsy moth populations are prone to cycles of boom and bust, so when caterpillar numbers are in check, the virus remains so as well.

  When gypsy moth invasions grow, the virus may go into outbreak mode, which serves as a natural control mechanism for caterpillar infestations. “This virus probably came to North America when the caterpillars did,” Hoover explained. “It’s just a natural enemy of the gypsy moth.”

  FUNGUS REARS ITS UGLY HEAD

  “Zombie” Ants

  Found With New Mind-Control Fungi

  A Brazilian rain forest is crawling with mind-controlled zombie ants whose brains are under the sway of a newly discovered fungus that controls their every move.

  There’s a new mind-controlling fungus in town, but you can rest easy, it only affects ants in a Brazilian rain forest. Originally thought to be a single species, called Ophiocordyceps unilateralis, the fungus is actually four distinct species—all of which can “mind control” ants—scientists announced.

  Four Fungi

  The fungus species can infect an ant, take over its brain, and then kill the insect once it moves to a location ideal for the fungi to grow and spread spores. All four known fungi species live in Brazil’s Atlantic rain forest, which is rapidly changing due to climate change and deforestation, said study leader David Hughes, an entomologist at Penn State University.

  Hughes and his colleagues made the discovery after noticing a wide diversity of fungal growths emerging from ant victims, according to the 2011 study in the journal PLoS ONE. “It is tempting to speculate that each species of fungus has its own ant species that it is best adapted to attack,” Hughes said.

  “This potentially means thousands of zombie fungi in tropical forests across the globe await discovery,” he said. “We need to ramp up sampling—especially given the perilous state of the environment.”

  TRUTH:

  AN ANT CAN CARRY 50 TIMES ITS BODY WEIGHT.

  Mmmm. Brains.

  Fire ants in South America must watch out for female phorid flies, which have a bizarre reproductive strategy: They hover over fire ants and then inject their eggs into the ants with a needlelike appendage. The egg grows, and the resulting larva generally migrates to the ant’s head. The larva lives there for weeks—slurping up the brain and turning the ant into a “zombie,” in some cases compelling the ant to march 55 yards (50 meters) away from its colony to avoid attack by other fire ants. Finally, the baby fly decapitates its host and hatches, exiting through the deceased ant’s head.

  How to Zombify an Ant

  The four newly identified “zombie” fungi species use different techniques to spread after infecting an ant, the researchers found. Some of the fungi species create thin “infection pegs” that stick out from a victim’s body and infect passing ants, Hughes said.

  Other fungus species develop explosive spores on infected ants’ bodies. When other ants come near the cadavers, the shooting spores can hit the unwitting passersby, turning them too into zombie ants.

  Once they are successfully lodged in a zombie ant’s brain, the fungi species “direct” the dying ants to anchor themselves to leaves or other stable places, providing a “nursery” for the fungus. For instance, as the Ophiocordyceps camponoti-balzani fungus is about to kill the ant, the insect bites down hard into whatever substance it’s standing on. This attachment is so strong that a dead zombie ant can remain stationary even when hanging upside down, the scientists say.

  The Cycle Begins Again

  The fungus will eventually kill the ant. Once it dies, the fungus rapidly spreads through the body. During the first couple days, though, very little evidence of the fungus is visible from the outside. But a few days after death, white fungus stalks begin to poke through the ant’s head. Also noticeable are faint, white, slightly fuzzy fungal growths on the ant’s joints.

  During later stages of Ophiocordyceps camponoti-rufipedis infection, the ant’s body takes on a furrier appearance as the fungus rapidly begins to colonize the outside of the ant’s body. In the final stages, a long fungus stalk continues to grow from the back of the head, becoming longer and more noticeable. The appearance of each stalk varies with each form of the fungus. For instance, Ophiocordyceps camponoti-rufipedis creates just a single stalk while Ophiocordyceps camponoti-balzani forms a forked stalk that resembles a reindeer’s antlers.

  TRUTH:

  A GIANT FUNGUS IN OREGON SPREADS OUT OVER AN AREA THE SIZE OF 20,000 BASKETBALL COURTS.

  Other Insects, Other Zombies

  Ants aren’t the only zombie-fungi hosts—other insects also fall prey to fungus. Crickets, wasps, and flies can all fall prey to different fungi. For instance, wasps can be infected by a Cordyceps fungus species that hasn’t yet been named or formally documented. Fungi of the Cordyceps genus are the products of a tightly evolved arms race between hosts and parasites, study author Hughes noted. That means the fungi are often locked into one type of host—a specialization that might spell doom for fungi species as host species die out.

  Much is left to be discovered about these fascinating fungi, and Hughes plans to remedy that—and expects to find many more zombie fungus species in the forests of Brazil. “This is only the tip,” he said, “of what will be a very large iceberg.”

  DOES SIZE MATTER?

  Cricket Has World’s Biggest Testicles

  (But Puny Output)

  The new title for world’s biggest testicles (relative to body weight) goes to the tuberous bushcricket, a type of katydid, according to a new study.

  The male tuberous bushcricket, a type of katydid, is now the record holder for the world’s biggest testicles relative to his size. But how does their size factor into the bug’s fertility?

  TRUTH:

  CRICKETS CAN SEE DIFFERENT DIRECTIONS AT THE SAME TIME.

  Production

  The sperm-producing organs account for 14 percent of the body mass of males of this bushcricket species. The previous record holder’s testicles—belonging to the fruit fly Drosophila bifurca—tipped the scales at about 11 percent of its body mass.

  “I was amazed by the size of the testes—they seemed to take up the entire abdomen,” said study leader Karim Vahed, a behavioral ecologist at the University of Derby in the United Kingdom.

  But the new heavyweight champion doesn’t pack much of a punch. The team was surprised to discover that tuberous bushcrickets have smaller ejaculations than bushcricket species with smaller testicles.

  Ideal Study Subjects

  For the testicle study, V
ahed and colleagues dissected specimens from 21 bushcricket species collected around Europe. The insects are ideal for studying reproductive evolution because of their efficient mating process, Vahed noted. For one thing, the male bushcricket transfers his sperm to the female in a “neat packet” that’s easily retrievable by researchers—“whereas in mammals, you’d have to provide some sort of condom to measure the ejaculate,” he said.

  Likewise the female stores each male’s sperm packet in a separate pouch, enabling scientists to count how many times a female has mated in her lifetime. Predictably, the team found that the species whose females mate the most has the males with the biggest testicles, according to the study, published in the journal Biology Letters.

  But among the 21 bushcricket species, the study showed that, as testicle size increases, ejaculation volume decreases. The discovery runs counter to previous findings in other species—especially mammals. Usually the male with the biggest testicles has more sperm in each ejaculation, thus earning him more tickets in the lottery of fertilizing females, Vahed explained.

  Strange Animal Genitalia Facts

  1. Carabid beetles have only one testicle—and scientists cannot explain why.

  2. Rodents with longer penises enjoy a mating advantage.

  3. Industrial pollutants are causing polar bears’ penises to shrink.

  4. Some female ducks have evolved vaginas with clockwise spirals that keep out oppositely spiraled penises of undesirable male ducks.

  5. Bats with larger brains have smaller testicles.

  Bigger Testicles, More Sperm?

  A possible explanation, he said, is that, in societies with promiscuous females, large testicles give males a more plentiful sperm reservoir for multiple matings. Female tuberous bushcrickets mate an average of 11 times in their two-month life spans. This alternative explanation for large testicles may even make scientists revisit some of their studies on vertebrates, he added. It’s usually the other way around.

  “It’s clear that insects are one of the major types of organisms on planet Earth, [but] the tendency is to draw conclusions from studies of vertebrates and generalize them as if they apply to everything,” he said.

  Indeed the take-home message for scientists is that mating rate needs to be taken into account when investigating testicle size, according to David Hosken, chair in evolutionary biology at the U.K.’s University of Exeter. Overall the findings are not that surprising, he added via email. “Higher mating rate selects for larger testes, but across other species, sperm competition risk seems to have a greater effect than mating rate.”

  TRUTH:

  FEMALE CRICKETS DO NOT CHIRP; A MALE GENERATES THE CHIRP SOUND WHEN HE RAISES HIS LEFT FOREWING AND RUBS IT AGAINST THE UPPER EDGE OF HIS RIGHT FOREWING.

  Bushcricket Titillator Mystery

  Next, Vahed plans to shift his focus to “titillators,” the hard, penislike part of male bushcricket genitalia that’s inserted into the female. These poorly studied—and often spiny—parts may stimulate the female, allow the male to hang on, or both.

  And, as it turns out, the tuberous bushcricket isn’t quite so well endowed in this arena. The species’ parts, he said, “don’t seem to be as outlandish as some species that have double sets of spiny titillators.”

  GOING UNDERGROUND

  New “Devil Worm”

  Is Deepest-Living Animal

  Deep within the earth lives the “devil worm,” a species evolved to withstand heat and crushing pressure at extreme depths.

  A “devil worm” has been discovered miles under the earth—the deepest-living animal ever found, a new study says. The new nematode species—called Halicephalobus mephisto partly for Mephistopheles, the demon of Faustian legend—suggests there’s a rich new biosphere beneath our feet.

  “If life arose on Mars and it is still there deep underground, then it may have continued to evolve into something more complex than we are willing to entertain today.”

  Gaetan Borgonie

  nematologist, University of Ghent

  Life Down Below

  Before the discovery of the signs of the newfound worm at depths of 2.2 miles (3.6 kilometers), nematodes were not known to live beyond dozens of feet (tens of meters) deep. Only microbes were known to occupy those depths—organisms that, it turns out, are the food of the 0.019-inch-long (0.5-millimeter) worm.

  “That sounds small, but to me it’s like finding a whale in Lake Ontario. These creatures are millions of times bigger than the bacteria they feed on,” said study co-author Tullis Onstott, a geomicrobiologist at Princeton University in New Jersey.

  Worm Evolved for Harsh Depths

  Onstott and nematologist Gaetan Borgonie of Belgium’s University of Ghent first discovered H. mephisto in the depths of a South African gold mine. But the team wasn’t sure if the worms had been tracked in by miners or had come out of the rock.

  To find out, Borgonie spent a year boring deep into mines for veins of water, retrieving samples, and filtering them for water-dwelling nematodes. He scoured a total of 8,343 gallons (31,582 liters) until he finally found the worm in several deep-rock samples.

  What’s more, the team found evidence the worms have been there for thousands of years. Isotope dating of the water housing the worm placed it to between 3,000 and 12,000 years ago—indicating the animals had evolved to survive the crushing pressure and high heat of the depths.

  “This discovery may not surprise passionate nematologists like Gaetan, but it’s certainly shocking to me,” Onstott said. “The boundary of multicellular life has been extended significantly into our planet.”

  TRUTH:

  THE DEEPEST LIVING FISHES EVER DISCOVERED ON EARTH ARE WHITE SNAILFISH FOUND 4.8 MILES BENEATH THE SURFACE OF THE PACIFIC OCEAN.

  Extreme Life on Earth and Elsewhere

  Onstott hopes the new devil worm will inspire others to search for complex life in the most extreme places—both on Earth and elsewhere. “People usually think only bacteria could exist below the surface of a planet like Mars. This discovery says, ‘Hold up there!’ ” Onstott said. “We can’t negate the thought of looking for little green worms as opposed to little green microbes.”

  FIRE ANTS UNITE!

  Fire Ants Swarm

  Form Life Raft

  The way that fire ants work together creates a whole new definition of teamwork. When the levee breaks, these creatures stick together.

  When a city floods, humans stack sandbags and raise levees. When a fire ant colony floods, the ants link up to form a literal life raft. Now, new research shows exactly how the ants manage this feat.

  Ants Ahoy!

  Engineering professor David Hu and graduate student Nathan J. Mlot at Georgia Institute of Technology had heard reports of ant rafts in the wild that last for weeks.

  “They’ll gather up all the eggs in the colony and will make their way up through the underground network of tunnels, and when the flood waters rise above the ground, they’ll link up together in these massive rafts,” Mlot said.

  Together with Georgia Tech systems-engineering professor Craig Tovey, the scientists collected fire ants and dunked clumps of them in water to see what would happen. In less than two minutes the ants had linked “hands” to form a floating structure that kept all the insects safe. Even the ants down below can survive this way, thanks to tiny hairs on the ants’ bodies that trap a thin layer of air. “Even when they’re on the bottom of the raft, they never technically become submerged,” Mlot said.

  TRUTH:

  1,000,000,000,000,000 (THAT’S ONE QUADRILLION) ANTS LIVE ON EARTH.

  Form a life raft! Fire ants link up to float on water. (Photo Credit 4.3)

  After watching the ants form rafts, the team froze the rafts in liquid nitrogen to study their structures. Ants had linked up using either a “hand to hand” grip, where each ant would grab another’s leg, or a mandible-to-leg grip.

  Either way, the formation of ant rafts is a delicate business: The maximum strength
by which two ants can grasp each other without causing harm is about 400 times their body weight, which is “significantly weaker than ant attachment to other complex surfaces,” the paper’s authors wrote.

  Different Floods, Different Rafts

  Ant rafts are quite buoyant, as the researchers found out after attempting, unsuccessfully, to sink one with a twig. During such “perturbations,” the ants contract their muscles, which makes the raft temporarily less buoyant but traps air better, preventing drowning.

  Ant Architects

  The fire ant is the only ant species that’s been observed forming rafts. But it’s been well known that several types of ants can form clusters to create structures similar to towers or bridges.

  The scientists created several other flooding scenarios to see how the ants would react. When a cluster of ants is just placed on the water, ants near the top try to leave the pile, Mlot said. But when an escaping ant reaches the edge and realizes that terra firma is nowhere to be found, “usually the ant will turn around and head back toward the center. By the time she realizes there’s an edge, there’s already another ant clambering on top of her, forcing that first ant to become part of the bottom layer.” In this way, ants that might have tried to survive solo are instead trapped into becoming part of the raft.