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This adult male bedbug wants to suck your blood. Photo: Armed Forces Pest Management Board

For thousands of years, humans have shared their beds with blood-sucking parasites. The ancient Greeks complained of bedbugs, as did the Romans. When the lights go off for those suffering from this parasitic infestation today, from under the mattress or behind the bedboard creeps up to 150,000 of the rice grain-sized insects (though average infestations are around 100 insects). While bedbugs are one of the few parasites that live closely with humans yet do not transmit a serious disease, they do cause nasty red rashes in some of their victims, not to mention the psychological terror of knowing that your body becomes a buffet for crawling bloodsuckers after dark. 

By the 1940s this age-old parasite was mostly eradicated from homes and hotels in the developing world. But around 1995, the bedbug tides again turned. Infestations began flaring up with a vengeance. Pest managers and scientists aren’t sure what happened, exactly, but it may have been a combination of people traveling more and thus increasing their chances of encountering bedbugs in run down motels or infested apartments; of bedbugs bolstering their resistance to common pesticides; and of people simply letting their guard down against the now unfamiliar parasites.

Large cities such as New York have particularly suffered from this resurgence. Since 2000, the New York Times has run dozens of articles documenting the ongoing plague of bedbugs, with headlines such as Even Health Dept. Isn’t Safe from Bedbugs and Bringing Your Own Plastic Seat Cover to the Movies.

As many hapless New Yorkers have found, detecting stealthy bedbugs is only the first step of what usually turns into a long, desperate eradication battle.  Most people have to combine both pesticides and non-chemical methods for purging their apartments. In addition to dousing the apartment and its contents in pesticides, this includes throwing away all furniture the bugs are living on (streetside mattresses in NYC with a “BEDBUGS!” warning scrawled across them are not an out-of-the-ordinary sight), physically removing the bodies of poisoned bugs, subjecting the home to extreme heat or cold, or even hiring a bedbug sniffing dog. Sometimes, after so many sleepless nights and days spent meticulously combing the cracks between the mattress and sheets or searching behind couch cushions, residents simply throw up their hands, move out and start their lives over.

Recognizing this ongoing problem, researchers are constantly trying to come up with new methods for quickly and efficiently killing the pests. The latest technique, described today in the Journal of the Royal Society Interface, takes a hint from mother nature and history. For years, people in Eastern Europe’s Balkan region have known that kidney bean leaves trap bedbugs, sort of like a natural fly paper. In the past, those suffering from infestations would scatter the leaves on the floor surrounding their bed, then collect the bedbug-laden greenery in the morning and destroy it. In 1943, a group of researchers studied this phenomenon and attributed it to microscopic plant hairs called trichomes that grow on the leaves’ surface to entangling bed bug legs. They wrote up their findings in “The action of bean leaves against the bedbug,” but World War II distracted from the paper and they wound up receiving little attention for their work.

Rediscovering this forgotten research gem, scientists from the University of California, Irvine, and the University of Kentucky set out to more precisely document how the beans create this natural bedbug trap and, potentially, how it could be used to improve bedbug purging efforts. “We were motivated to identify the essential features of the capture mechanics of bean leaves to guide the design and fabrication of biomimetic surfaces [or synthetic materials that mimic ones found in nature] for bed bug trapping,” they write in their paper.  

Images of bed bug legs (yellow) on bean leaf surfaces with hooked trichomes (green). Scanning electron microscope photo from The Royal Society

They used a scanning electron microscope and video to visualize how the trichomes on the leaves stop the bedbugs in their ravenous tracks. Rather than a Velcro-like entanglement as the 1943 authors had suggested, it seems that the leaves stick into the insects’ feet like giant thorns, physically impaling the pests.

Knowing this, the researchers wondered if they could improve upon the method as a way to treat bedbug infestations, because leaves themselves dry out and can’t be scaled up to larger sizes. “This physical entrapment is a source of inspiration in the development of new and sustainable [or scalable and chemical-free] methods to control the burgeoning numbers of bed bugs,” they write.

They used fresh bean leaves as a template for micro-fabricating produced surfaces that precisely mimicked the leaves. To do this, they created a negative molding of the leaves, then poured in polymers sharing a similar material composition of the living plant’s cell walls.

Fabrication of biomimetic surfaces (d and e) from bean leaves (b and c). (1–3) A negative molding material is poured onto a leaf surface, and pressure is applied. (4–6) The leaf is removed, and the negative mold is filled with the positive replica material. (7) The negative mold is removed leaving the replica. Image from The Royal Society

The team then allowed bedbugs to walk across their synthetic leaves to test their effectiveness compared to the real deal. The fabricated leaves did snag the bugs, but they didn’t hinder the insects’ movements quite as effectively as the living plants. But the researchers are not deterred by these initial results. They plan to continue working on the problem and improving their product by more precisely incorporating the mechanical properties of the living trichomes. The optimistically conclude: 

With bed bug populations skyrocketing throughout the world, and resistance to pesticides widespread, bioinspired microfabrication techniques have the potential to harness the bed bug-entrapping power of natural leaf surfaces using purely physical means.

Researchers used miniature robots to mimic how real ants maneuver networks of their own. Credit: Simon Garnier, et al

For ants, the pheromone-laden foraging trails they leave behind are like lifelines: they direct the workers toward food hubs discovered earlier and help guide them home back to their nest.

These networks of trails can stretch for hundreds of feet, quite the achievement considering many worker ants are less than half an inch in length. One type of harvester ant can lay down a set of trails (PDF) that stretch 82 feet from the entrance of its nest. The trails of a wood ant, an insect measuring just five millimeters (that’s one-fifth of an inch), reach 656 feet, each one branching out into more pathways at up to 10 spots on each trail. The leafcutter ant can build a network that spreads for almost two and a half acres.

Ant species such as these tend to take the shortest path between their colony’s nest and a food source, following branches that stray as little as possible from the direction in which they began their journey. The forks in their network of trails, known as bifurcations, are not symmetrical and don’t branch out into angles of the same size. But do ants use a sophisticated sense of geometry to trace their path, measuring the angles of the roads before picking one?

To learn more, researchers at the New Jersey Institute of Technology (NJIT) and the Research Centre on Animal Cognition in France used miniature robots to replicate the behavior of a colony of Argentine ants on the move, reported today in the journal PLOS Computational Biology. This ant species has extremely poor eyesight and darts around at high speeds, yet it can maneuver through corridor after corridor, from home to food and vice versa.

When no obstacles are around, ants prefer to walk in a straight line without deviating from their course. People are like that too: if we were walking down a street to a restaurant that’s on the same side of the road as we are, we wouldn’t cross to the opposite sidewalk unless something was blocking our way. To imbue this sense of obstacle avoidance into the robots, researchers programmed them to avoid obstacles and follow light trails, which the researchers used as a substitute for pheromone-coated paths.

An “Alice,” a tiny robot measuring two centimeters (just less than one inch), following a trail of light using two photoreceptors. Credit: Simon Garnier, et al

The 10 tiny robots in this study, called Alices, were then tasked to navigate a maze-like environment roughly 60 to 70 times their size, from a starting point representing a nest entrance to an end point signifying a food source. Two photoreceptors, mimicking ant antennae, detected beams of light. As the robots traveled through the maze, researchers introduced a wrench in the little machines’ plans—at random points in their journey, the robots were triggered to turn, a mechanism meant to further mimic ants’ meandering gaits as they creep along their paths. These random turns rotated at angles no greater than 30 degrees, as real ants are not very efficient at physically making U-turns.

In the sped-up video below, the researchers tested the Alices’ navigation skills in a complex network, charging them with choosing the shortest route between their “nest” (on the right) to a “food source (left). Varying beams of light projected onto the maze changed the robots’ movements inside the network as their photoreceptors kicked into action.

The researchers found that, without any knowledge of the geometry of the maze, the robotic ants behaved exactly as real ants do: they made small random turns, but moved in the same general direction. When they reached a fork in the road, this led the robots to choose the path that deviated least from their initial trajectory, even though they weren’t equipped to measure any angles. When they detected a light trail, they turned to follow that path.

The researchers say this means that Argentine ants may not need to use complex cognitive processes to compute the geometry of various trails. But taking the fork in the road that leads to the shortest route to food greatly increases foraging success for an entire colony. So using pheromones with an intuitive spatial knowledge of where food may be, keeps ants on the right track; as more ants follow the path to food, pheromones become more concentrated along the path, further helping to guide ants who have yet to travel. In fact, the navigation method of choosing the correct fork in the road triples the amount of food ants bring back to their nest than if they relied on pheromones alone, says lead author Simon Garnier, a biology professor at NJIT.

“If you have only the pheromones and you don’t have this trick, you’re less efficient because you’re more likely to get the ants trapped into loops,” says Garnier, who runs the institute’s Swarm Lab, which studies insect group behavior. “So they will reinforce their path around the loop, and they’ll just get stuck in this loop and turn and turn forever.”

Such navigation may also help guide ants through underground paths that connect different parts of their nests. Replicating these natural navigation tools allows researchers to better understand the inner-workings of collective animal behavior.

Dead locusts litter Israel’s Negev desert after being sprayed with pesticide on Wednesday. Photo: Rachel Nuwer

Locusts have plagued farmers for millennia. According to the Book of Exodus, around 1400 B.C. the Egyptians experienced an exceptionally unfortunate encounter with these ravenous pests when they struck as the eighth Biblical plague. As Exodus describes, “They covered the face of the whole land, so that the land was darkened, and they ate all the plants in the land and all the fruit of the trees that the hail had left. Not a green thing remained, neither tree nor plant of the field, through all the land of Egypt.”

Locusts attacks still occur today, as farmers in Sudan and Egypt well know. Now, farmers in Israel can also join this unfortunate group. Earlier today, a swarm of locusts arrived in Israel from Egypt, just in time for the Jewish Passover holiday which commemorates Jews’ escape from Egyptian slavery following the ten Biblical plagues. “The correlation with the Bible is interesting in terms of timing, since the eighth plague happened sometime before the Exodus,” said Hendrik Bruins, a researcher in the Department of Man in the Desert at Ben-Gurion University of the Negev in Israel. “Now we need to wait for the plague of darkness,” he joked.

With the help of the Lord, Moses delivers a plague of locusts upon the Egyptians, seen in the photo of a Bible page above. Photo via New York Public Library, Renaissance and medieval manuscripts collection

While the timing is uncanny, researchers point out that–at least in this case–locust plagues are a normal ecological phenomenon rather than a form of divine punishment. “Hate to break it to you, but I don’t think there’s any religious significance at all to insects in the desert, even a lot of them, and even if it seems reminiscent of a certain Biblically described incident,” said Jeremy Benstein, deputy director of the Heschel Center for Sustainability in Tel Aviv.

In this region of the world, locusts swarm every 10 to 15 years. No one knows why they stick to that particular cycle, and predicting the phenomena remains challenging for researchers. In this case, an unusually rainy winter led to excessive vegetation, supporting a boom in locust populations along the Egyptian-Sudanese border. As in past swarms, once the insect population devours all of the local vegetation, the hungry herbivores take flight in search of new feeding grounds. Locusts–which is just a term for the 10 to 15 species of grasshoppers that swarm–can travel over 90 miles in a single day, carried by the wind. In the plagues of 1987 and 1988 (PDF)–a notoriously bad period for locusts–some of the befuddled insects even managed to wash up on Caribbean shores after an epic flight from West Africa.

When grasshoppers switch from a sedentary, solo lifestyle to a swarming lifestyle, they undergo a series of physical, behavioral and neurological changes. According to Amir Ayali, chair of the Department of Zoology at Tel Aviv University, this shift is one of the most extreme cases of behavioral plasticity found in nature. Before swarming, locusts morph from their normal tan or green coloring to a bright black, yellow or red exoskeleton. Females begin laying eggs in unison  which then hatch in synch and fuel the swarm. In this way, a collection of 1 million insects can increase by orders of magnitude to 1 billion in a matter of months.

From there, they take flight, though the exact trigger remains unknown. Labs in Israel and beyond are working on understanding the mathematics of locust swarming and the neurological shifts behind the behaviors that make swarming possible. ”If we could identify some key factors that are responsible for this change, we could maybe find an antidote or something that could prevent the factors that transform innocent grasshoppers from Mr. Hyde to Dr. Jekyll,” Ayali said. “We’re revealing the secrets one by one, but there’s still so much more to find out.”

A swarm of locusts will consume any green vegetation in its path–even toxic plants–and can decimate a farmer’s field almost as soon as it descends. In one day, the mass of insects can munch its way through the equivalent amount of food as 15 million people consume in the same time period, with billions of insects covering an area up to the size of Cairo, Africa’s largest city. As such, at their worst locust swarms can impact some 20 percent of the planet’s human population through both direct and indirect damages they cause. In North Africa, the last so-called mega-swarm invaded in 2004, while this current swarm consists of a measly 30 to 120 million insects. 

Estimating the costs exacted by locusts swarms remains a challenge. While locust swarms reportedly cause more monetary damage than any other pest, it’s hard to put an exact figure on the problem. Totaling the true crost depends on the size of the swarm and where the winds carry it. To be as accurate as possible, costs of pesticides, food provided to local populations in lieu of wrecked crops, monitoring costs and other indirect effects must be taken into account. No one has yet estimated the cost of this current swarm, though the United Nation’s Food and Agriculture Organization (FAO) allots $10 million per year solely to maintain and expand current monitoring operations.

Locusts covering a bush during the 2004 swarm near the Red Sea cost in Israel. Photo: Amir Ayali

This morning, the Israeli Ministry of Agriculture sprayed pesticides on an area of around 1,000 hectares near the Egyptian border. To quell a plague of locusts, pest managers have to hit the insects while they’re still settled on the ground for the night and before they take flight at dawn. So far, pesticide spraying is the only option for defeating the bugs, but this exacts environmental tolls. Other invertebrates, some of them beneficial, will also shrivel under the pesticide’s deadly effects, and there’s a chance that birds and other insectivores may eat the poisoned insect corpses and become ill themselves. Researchers are working on ways to develop fungus or viruses that specifically attack locusts, but many of those efforts are still in initial investigative stages. However, the company Green Muscle developed a commercially available fungus that affects only locusts.

Even better, however, would be a way to stop a swarm from taking flight from the very beginning. But this requires constant monitoring of locust-prone areas in remote corners of the desert, which is not always possible. And since the insects typically originate from Egypt or Sudan, politics sometimes get in the way of quashing the swarm before it takes flight. “We really want to find them before they swarm, as wingless nymphs on the ground,” Ayali said. “Once you miss that window, your chances of combating them are poor and you’re obliged to spray around like crazy and hope you catch them on the ground.”

In this case, Egypt and Israel reportedly did not manage to coordinate locust-fighting efforts to the best of their abilities. “If you ask me, this is a trans-boundary story,” said Alon Tal, a professor of public policy at Ben-Gurion University. “This is not a significant enemy–with an arial approach you can nip locusts in the bud–but the Egyptian government didn’t take advantage of the fact that they have quite a sophisticated air force and scientific community just to the north.”

Ayali agrees that the situation could have been handled better. He also sees locusts as a chance to foster regional collaboration. Birders and ornithologists from Israel, Jordan and Palestine often cooperate in monitoring migratory avian species, for example, so theoretically locusts could likewise foster efforts. “Maybe scientists should work to bridge the gaps in the region,” Ayali said. “We could take the chance of this little locust plague and together make sure we’re better prepared for the next.”

For now, the Israelis have smote the swarm, but Keith Cressman, a senior locust forecasting office at the FAO’s office in Rome warns that there is still a moderate risk that a few more small populations of young adults may be hiding out in the desert. This means new swarms could potentially form later this week in northeast Egypt and Israel’s Negev region. His organization warned Israel, Egypt and Jordan this morning of the threat, and Jordan mobilized its own locust team, just in case.

For those who do come across the insects (but only the non-pesticide covered ones!), Israeli chefs suggest trying them out for taste. Locusts, it turns out, are the only insects that are kosher to eat. According to the news organization Haaretz, they taste like “tiny chicken wings,” though they make an equally mean stew. “You could actually run out very early before they started spraying and collect your breakfast,” Ayali said. “I’m told they’re very tasty fried in a skillet, but I’ve never tried them myself.”

A swarm of locusts descends upon Israel. Photo by Amir Ayali

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Wild bees, such as this Andrena bee visiting highbush blueberry flowers, provide crucial pollination services to crops across the globe. Photo by Daniel Cariveau

Insect pollination is crucial for the healthy development of our favorite foods, from apples and avocados to cucumbers and onions. Of the 100 crop species that provide 90 percent of the global population’s food, nearly three-quarters rely on pollination by bees. The rest need beetles, flies, butterflies, birds and bats to act as pollinators. It’s a mutually beneficial system—the flowers of most crops require pollen from another plant of the same crop to produce seeds or fruits, and bees and other critters transfer pollen from one plant to the next as they drink a flower’s nectar.

The agriculture industry relies on both wild pollinators and human-managed ones like honeybees, kept and cared for in hives across the country. Concern over the latter’s gradual decline has grown in recent times, but new research shows it might be the wild pollinators we should be worrying about.

In a study of 600 fields of 41 major crops (fruits, grains and nuts) on six continents, published today in the journal Science, researchers found that wild insects pollinate these crops more effectively than honeybees that are in the care of humans. In fact, compared to bees living in apiaries, wild pollinators lead to twice as much of what’s called “fruit set”—the amount of flowers that develop into mature fruits or seeds.

Pollination is essential for the production of fruits like cherries, cranberries and blueberries. Blueberries, along with tomatoes, especially depend on buzz pollination, a process by which bees vibrate their flight muscles rapidly to unleash a visible cloud of pollen into a flower. Honeybees aren’t capable of this kind of pollination, says lead study author Lucas Garibaldi, a professor at the National University of Río Negro in Argentina. Of all pollinator-dependent crops, approximately 8 percent require buzz pollination, he says.

Pollination, then, is central to ensuring our both our food staples and our varied diet.“These ecosystem services are free, but they’re important for our survival,” Garibaldi adds. “They need to be promoted and maintained if we want to continue living on this planet.”

Another new study found that wild bee population, as well as the number of different species of the insects, has plummeted over the last 120 years. Researchers used observations of interactions between plants and their pollinators in Illinois collected at three points in time: in the late 1800s, the 1970s and the first decade of this century. Of the 109 bee species seen visiting 26 woodland plants in the 19th century, only 54 remained by 2010. Rising temperatures caused mismatches in peak bee activity, measured by visits to different plants, and flowering times, a break in the delicate balance of insect-plant relationship.

Less diversity in the wild bee population meant fewer interactions between flowers, a change that in the agricultural world could result in smaller crop yields, says lead author Laura Burkle, an ecology professor at Montana State University. This throws off global agriculture production and speeds up land conversion to compensate for the loss.

“Things have changed for the worst,” Burkle says. “There’s an incredible amount of robustness within these interaction networks of species that allow them to persist in the face of really strong environmental changes, both in temperature and land-use change.” Unfortunately, these pollinators are “getting punched from a variety of sides,” she adds.

Can honeybees substitute for our disappearing wild pollinators? Garibaldi and colleagues found that these insects couldn’t fully replace the contributions of diverse populations of pollinators for a wide range of crops on farmlands on every continent. Flooding farmland with human-managed honeybees only supplemented pollination by wild insects, even for crops such as almonds, whose orchards are stocked routinely with bees.

Human-managed hives stocked with bees, ready to aid in pollination at an almond grove. Photo by Daniel Cariveau

Several culprits are behind the continuing decline of these wild pollinators. The insects usually live in forests and grasslands, and continuing conversion of such natural habitats into farmland results in shrinking numbers and types of wild pollinators, meaning fewer flowers receive the pollen necessary for reproduction. 

Last year, many plants in the eastern U.S. flowered a month earlier than any other time in the last 161 years, a result of such unusually warm weather. Burkle says bee development doesn’t always catch up to changing flowering times in plants, which leads to more mismatches in interaction and decreased pollination services. Another study in the same year found that elevated levels of carbon dioxide, combined with the use of nitrogen-infused fertilizer, altered some plants’ lifetime development. The toxic pairing led them to produce flowers with nectar more attractive to bumblebees than usual, but caused the plants to die sooner.

The waning insect population has already taken a measurable toll on crop production, including on one very near and dear to our hearts: coffee. A 2004 study of coffee pollination in Costa Rica found that when numbers of human-introduced honeybees shrunk in a given forest area, diverse pollinators native to the area, such as stingless bees known as meliponines native to the area, helped compensate for the loss. But these insects couldn’t survive at the edges of the forest like honeybees could, so the production of coffee, a crop highly dependent on pollination, eventually plummeted.

“This study supports the theoretical prediction that having many different species, which each respond to the environment in slightly different ways, is like having a stock portfolio from many different companies, rather than investing all your money in a single company’s stock,” explains Jason Tylianakis, a terrestrial ecology professor at the University of Canterbury in New Zealand. Tylianakis discussed the implications of Science’s two new studies in a paper also published today. “We should expect this kind of ‘insurance effect’ to become less common as more native pollinators go extinct.”

Given the mounting evidence, Tylianakis writes in an email that concerns about a global pollination crisis are not overstated. A changing climate, the rapid spread of farmland and a reliance on pesticides means diverse, wild pollinators will continue to face challenges as this century unfolds. If pollinators are dying out worldwide—and if pace of this die out continues with the variety of species getting cut in half each century, leaving behind less effective substitutes—food production as we know it could start to crumble.

“The bottom line is that we need biodiversity for our survival, and we can’t simply replace the services provided by nature with a few hand-picked species like the honeybee,” he says.

A male human head louse. Photo by Flickr user Gilles San Martin

Parasites have been around for more than 270 million years. Around 25 million years ago, lice joined the blood-sucking party and invaded the hair of ancient primates. When the first members of Homo arrived on the scene around 2.5 million years ago, lice took advantage of the new great ape on the block for better satisfying its digestive needs. As a new genetic analysis published today in PLoS One shows, mining these parasites’ genomes can lend clues for understanding the migration patterns of these early humans.

The human louse, Pediculus humanus, is a single species yet members fall into two distinct camps: head and clothing lice–the invention of clothing likely put this divide into motion. Hundreds of millions of head lice infestations occur each year around the world, most of them plaguing school-aged children. Each year in the United States alone, lice invade the braids and ponytails of an esimtated 6 to 12 million kids between the ages of 3 to 11. Clothing lice, on the other hand, usually infect the homeless or people confined to refugee camps. Clothing lice–also referred to as body lice–are less prevalent but potentially more serious because they can serve as vectors for diseases such as typhus, trench fever and relapsing fever.

Researchers have studied the genetic diversity of head and clothing lice in the past, but scientists from the Florida Museum of Natural History at the University of Florida decided to tap even deeper into the parasites’ genome, identifing new sequences of DNA that could be used as targets for tracking lice evolution through time and space. From these efforts, they found 15 new molecular markers, called microsatellite loci, which could help uncover the genetic structure and breeding history behind different lice populations–and potentially their corresponding humans of choice.

Using those genetic signals, they analyzed the genotypes of 93 human lice taken for 11 different sites around the globe, including North America, Cambodia, Norway, Honduras, the UK and Nepal, among others. They collected lice from homeless shelters, orphanages and lice eradication facilities.

Inbreeding, it turned out, is common in human lice around the world. Lice in New York City shared the most genetic similarities, pointing to the highest levels on inbreeding from the study samples. Clothing lice tended to have more diversity than head lice, perhaps due to an inadvertent bottlenecking of the head lice population due to high levels of insecticides those parasites are regularly exposed to. As a result of repeated run-ins with anti-lice shampoos and sprays, only the heartiest pests would survive, restraining the overall diversity of the population. Insecticide resistance is a common problem in head lice, but less of an issue with clothing lice. The authors identified one possible gene that may be responsible for much of the head louse’s drug resistance, though further studies will be needed to confirm that hunch. 

The researchers also analyzed lice diversity to see how it relates to human migration. They found four distinct genetic clusters of lice: in clothing lice from Canada, in head lice from North America and Europe, in head lice from Honduras and in all Asian lice.

Here’s the authors present a map of lice genetic diversity. The colored circles indicate sampling sites, with the different colors referring to the major genetic clusters the researchers identified. The grey flowing arrows indicate proposed migrations of modern humans throughout history, and the colored arrows represent the hypothetical co-migration of humans and lice.

Photo from Ascunce et al., PLoS One

How this geographic structure reflects human migration, they write, will require more sampling. For now, they can only speculate about the implications:

Although preliminary, our study suggests that the Central America-Asian cluster is mirroring the (human host) colonization of the New World if Central American lice were of Native American origin and Asia was the source population for the first people of the Americas as has been suggested. The USA head louse population might be of European decent, explaining its clustering with lice from Europe. Within the New World, the major difference between USA and Honduras may reflect the history of the two major human settlements of the New World: the first peopling of America and the European colonization after Columbus.

Eventually, genetic markers in lice could help us understand interactions between archaic hominids and our modern human ancestors, perhaps answering questions such as whether or not Homo sapiens met with ancient relatives in Asia or Africa besides Homo neanderthalensis. Several kinds of louse haplotypes, or groups of DNA sequences that are transmitted together, exist. The first type originated in Africa, where its genetic signature is strongest. A second type turns up in the New World, Europe and Australia, but not in Africa, suggesting that it may have evolved first in a different Homo species whose base was in Eurasia rather than Africa. If true, then genetic analysis may give us a time period for when humans and other Homo groups for came into contact. And if they interacted close enough to exchange lice, perhaps they even mated, the researchers speculate.

So not only can the genetic structure of parasite populations help us predict how infections spread and where humans migrated, it may give insight into the sex-lives of our most ancient ancestors.