Caption: A phorid fly hovers above a fire ant before laying an egg in the ant’s thorax. Fire ant venom attracts the flies to the ants, scientists report.

S. Porter/USDA-ARS

Consider the case of fire ants and phorid flies. Fire ants are venomous pests that roam the southeastern United States and pack a powerful punch with their bite. Phorid flies are tiny bugs, half the size of a grain of rice. When a phorid fly lands on a fire ant, it deposits eggs in the ant’s chest. An egg hatches, and the fly pupa makes its way to the ant’s head.

And cuts the ant’s head off.

Scientists have known for years that flies can decapitate ants, but they didn’t know how the flies were able to find the unlucky ants in the first place. According to a recent study, the flies track the ants by tracking chemicals from a surprising source: the ants’ venom. In other words, the fire ants’ own poison works against them.

The study was led by Henry Fadamiro, an entomologist at Auburn University in Alabama. An entomologist is a scientist who studies insects. Fire ants give off a wide range of different chemicals, and Fadamino and his team wanted to know which of these chemicals attracted the flies.

In their experiment, they attached small electrodes to the antennae of the flies and then exposed the flies’ antennae to different chemicals from fire ants. These electrical devices were able to detect signals from the nervous systems of the flies. As a result, they were able to determine which chemicals caused the flies to get excited.

This decapitated fire ant was a victim of a tiny fly whose young eat the ants from the inside out, eventually beheading them.

S. Porter/USDA-ARS

The flies responded to chemicals from the venom of the fire ants. Fadamiro and his team then separated the venom into its different chemical components and tested those chemicals as well. They wanted to know which specific chemical compounds the flies liked best. The venom is mostly made up of alkaloids, which are chemical compounds that contain nitrogen and can be poisonous.

Fadamiro’s research may result in a new way to control the fire ant population in the United States. By understanding what makes phorid flies tick, scientists may be able to figure out how to attract them to areas—say, where fire ants thrive. If phorid flies can be introduced to these areas, they may help take the sting out of fire ant infestations.

“We hope if we get the right combination, that these … methods will begin to really make a difference,” says Sanford Porter, a fire ant specialist with the U.S. Department of Agriculture’s Agricultural Research Service in Gainesville, Fla.

Fadamiro’s research also explores how gruesome some animals can be. And even though this science is not just a Halloween curiosity, it may inspire a spooky holiday. For a scary costume this year, why not grab a friend and go as a naturally creepy duo: the headless fire ant and the phorid fly?

POWER WORDS

venom A poisonous secretion of an animal, such as a snake, spider, or scorpion, usually transmitted by a bite or sting

gland A cell, a group of cells, or an organ that produces a secretion for use elsewhere in the body or in a body cavity or for elimination from the body

chemical A substance with a distinct molecular composition that is produced by or used in a chemical process

electrode A solid electric conductor through which an electric current enters or leaves an electrolytic cell or other medium.

alkaloid Any of various organic compounds, normally with basic chemical properties and usually containing at least one nitrogen atom. Many alkaloids, such as nicotine, quinine, cocaine, and morphine, are known for their poisonous or medicinal attributes.

nitrogen A nonmetallic element that constitutes nearly four-fifths of the air by volume, occurring as a colorless, odorless, almost inert diatomic gas, N2, in various minerals and in all proteins and used in a wide variety of important manufactures, including ammonia, nitric acid, TNT, and fertilizers.

pupa The nonfeeding stage between the larva and adult in the metamorphosis of some insects

Going Deeper:

Chances are, though, you’ve come face-to-face with plenty of these crusty, leafy, or shrubby growths. Lichens live on rocks, branches, houses, even metal street signs. You can find these often colorful organisms almost everywhere—from deserts to rainforests, Antarctica to Africa. They’ve survived trips to outer space, and some scientists suspect there might even be lichens on Mars.

“If you go into your backyard, you will definitely find a lichen somewhere,” says Imke Schmitt, a lichen researcher—called a lichenologist—at the University of Minnesota, Twin Cities.

What you probably don’t realize is that a lichen is more than a single thing. It is a thriving relationship between two different types of living organisms: a fungus and an alga. Neither of these organisms is a plant, so the lichen isn’t a plant either.

Different species of lichens can look very different from each other. Thorsten Lumbsch, a lichenologist at The Field Museum in Chicago, took photographs of two varieties of lichens—a rock lichen (above) and a spot lichen (below)—during a recent

Thorsten Lumbsch

Thorsten Lumbsch

Through photosynthesis, the alga harvests the sun’s energy to make food for the fungus, which provides a place for the alga to live. But the relationship is lopsided, Schmitt says, with algae caged like prisoners—even slaves—inside their fungal hosts.

Around the world, scientists have identified tens of thousands of types of lichens. At least as many probably still await discovery, says Thorsten Lumbsch, a lichenologist at the Field Museum in Chicago.

“Even in North America, there is a huge lack of knowledge” about lichen diversity and biology, Lumbsch says. “There’s a lot still to discover.”

As lichenologists continue to find new species of lichens, they are also working to understand how various species are related to one another. By putting together a lichen family tree, they hope to understand why so many different types of lichens have evolved in so many places around the world.

Most research involves attempts to understand basic facts about the organisms and their interrelationships. But researchers are also teaming up with lichens to monitor the health of the environment, among other applications.

Tough work

Studying lichens is rarely easy. Most species depend on very specific conditions, and scientists can rarely get them to grow in laboratories. This provides lichenologists a great excuse to travel around the world, scouting new specimens and insights.

Lumbsch, for one, makes several trips to Australia and South America each year. In the field, he searches for a group of crusty lichens that tends to be quite tiny—usually less than a few millimeters long. Finding samples takes patience and a trained eye.

“You have to look very closely,” Lumbsch says. “Usually, I know which species I’m interested in and which habitats they grow in. So, I go there and crawl on my knees on the forest floor with a hand lens.”

Like many lichenologists, Lumbsch (far right) travels all over the world to collect specimens. This photograph was taken on a research trip to India in January 2008.

Thorsten Lumbsch

Spotting lichens is challenging enough. Identifying them is even harder. Many species look exactly alike, even when they are only distant cousins. Closely related species, meanwhile, can live in totally different environments, or on opposite ends of the Earth. (One species, for example, is found only near both poles.)

When they’re done collecting samples, lichenologists bring their catch back to the lab. Under a microscope, the researchers classify samples by structure and color. Then, they grind specimens into a powder, from which they extract genetic material. These DNA molecules, which appear in all cells, make up genes, which determine how organisms look and work.

The more closely related two organisms are, the more similar their DNA will be. Comparing DNA from different species, then, can give scientists an idea of when each group split off from a common ancestor. Researchers use this information to build lichen family trees that depict kinship between species.

“Once we have these trees, we can ask a lot of interesting questions,” Schmitt says.

For example, family trees can help explain what the first lichens looked like, how they have evolved over time, and how far any given species has moved around the globe. Such insights should provide a window into our planet’s distant past. Some researchers think that lichens were the first organisms to live on land, long before plants evolved to do so.

“[Lichens] have an extremely long history,” Schmitt says. “This is what we are trying to uncover by building family trees.”

The work is slow going, she adds. “But we are beginning to see a picture emerging.”

Environmental police

Despite their reputation as scientific curiosities, lichens have a practical side. Throughout history, people have used different species to make dyes for fabrics, poisons for arrowheads, and “green”-smelling scents for perfumes. Birds use lichens to make nests. Reindeer and other animals, including some people, eat them. (Don’t try this at home—some species taste awful!)

In modern times, scientists have found a new role for these growths: as environmental watchdogs.

Although lichens can live in some of the harshest environments on Earth, Schmitt notes that they “are very sensitive to any kind of change that humans put on the environment.”

Some species of lichen are highly sensitive to changes in the environment.

Tsnena/Wikipedia

Studies show that some species quickly disappear when exposed to air pollution. These sensitive types also suffer from habitat loss due to logging, construction, or other environmental disturbances. The presence of lichens in an ecosystem, then, generally signals that the air is clear and the environment healthy. Their disappearance, on the other hand, can be a warning sign.

Lichens are good monitors of air quality. In fact, studies have shown higher rates of lung cancer in people who live in areas where sensitive lichens have died off. As a result, Lumbsch says, some European cities require developers to confirm the presence of sensitive lichens as a sign of habitable air quality before building new homes. Where lichens reside, city planners can feel confident that homeowners will have good air to breathe.

Among other projects, Lumbsch and his colleagues are looking at the effects of climate changes on lichen populations. Some day, he says, lichens might add service as global-warming sentinels to their list of accomplishments.

Lichens have long been overlooked. Chat with a lichenologist, though, and you’ll find plenty about these underappreciated growths to like, if not love!

Additional Information

Word Find: Lichens—What’s not to like?

Going Deeper: