Category: Invasive species

To control cannibal toads, you just need the right bait

By Ed Yong | June 13, 2012 9:00 am

Australians love to destroy cane toads. Ever since these animals were first introduced in 1935, they have run amok, eating local animals and poisoning any that try to eat them. They’re captured and slaughtered in traps, bludgeoned with golf clubs, and squished with veering tyres, but still they continue to spread. Now, Michael Crossland from the University of Sydney has discovered an unlikely ally in the quest to control the cane toad: the cane toad.

Along with their unappealing appearance and milky poison, cane toads are also cannibals. Older tadpoles will hunt and eat eggs that have been recently laid in the same pond, to do away with future competitors. Crossland reasoned that the eggs must release a substance that the tadpoles can detect, so he mushed them up in his lab and separated out their chemical components.

He discovered that the eggs secrete bufadienolides – the same substances that make the milky poisons of the adult toads so deadly to Australia’s fauna. Ironically, the same chemicals that protect the eggs later in life also attract cannibalistic tadpoles. And that makes them excellent bait.

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Scientists and tourists bring thousands of alien seeds into Antarctica

By Ed Yong | March 5, 2012 3:00 pm

Aliens are invading Antarctica. Thanks largely to scientists, they have already established a foothold on the frozen continent, and their numbers are set to increase. This might sound like the plot of John Carpenter’s classic film The Thing, but it is very real.

The aliens in question are not body-snatching monsters, but plants from other parts of the world. Steven Chown from Stellenbosch University found that in just one summer, visitors unwittingly imported around 70,000 seeds to Antarctica. And even though the continent has a reputation for being harsh and desolate, many of these immigrants have already founded populations in their new homes.

This is a new chapter in an old story. Wherever humans go, seeds hitch a lift on our clothes and belongings. If these foreigners germinate where they don’t belong, they can often out-compete native plants and uproot local ecosystems. From Japanese knotweed to kudzu vines, these invasive species cause problems throughout the world. Inhospitable though Antarctica is, it’s not immune to such invasions. It does, however, present a valuable opportunity to study them.

In most cases, we can only see the results of plant invasions when it’s too late. We know that many species are brought into new places accidentally, but it’s hard to quantify how often this happens. You can hardly stop everyone entering a country and count the number of seeds that they’re carrying. Except when you can. Travel to Antarctica is so limited that Chown managed to stop 2 per cent of all the visitors in a single summer and count the number of seeds on their persons and belongings.

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CATEGORIZED UNDER: Environment, Invasive species

Beetle pest destroys coffee plants with a gene stolen from bacteria

By Ed Yong | February 27, 2012 3:00 pm

For fans of a velvety latte or a jolting espresso, meet your greatest enemy: the coffee berry borer beetle. This tiny pest, just a few millimetres long, can ruin entire coffee harvests. It affects more than 20 million farming families, and causes losses to the tune of half a billion US dollars every year- losses that are set to increase as the world warms.

But the beetle isn’t acting alone. It has a secret weapon, stolen from an unwitting accomplice.

Ricardo Acuña has found that the beetle’s ancestors pilfered a gene from bacteria, most likely the ones that live in its gut. This gene, now on permanent loan, allows the insect to digest the complex carbohydrates found in coffee berries. It may well have been the key to the beetle’s global success.

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Since pythons invaded, Florida’s mammal populations have crashed

By Ed Yong | January 30, 2012 3:00 pm

It turns out that if you unleash giant snakes into a place that didn’t previously have giant snakes, the other local animals don’t fare so well. That seems obvious, but you might be surprised at just how badly those other animals fare.

Since 2000, Burmese pythons have been staging an increasingly successful invasion of Florida. No one knows exactly how they got there. They normally live in south-east Asia and were probably carried over by exotic wildlife traders. Once in America, they could have escaped from pet stores or shipping warehouses. Alternatively, overambitious pet owners could have released when they got too large for comfort. Either way, they seem to be thriving.

With an average length of 12 feet (4 metres), the pythons are formidable predators. They suffocate their prey with powerful coils, and they target a wide variety of mammals and birds. The endangered Key Largo woodrat and wood stork are on their menu. So are American alligators (remember this oft-emailed photo?). Conservationists are trying to halt the spread of the giant snakes, out of concern that their booming numbers could spell trouble for local wildlife.

Michael Dorcas from Davidson College thinks they are right to be concerned. In the first systematic assessment of the pythons’ impact, Dorcas has found that many of Florida’s mammals have plummeted in numbers in places where the snakes now live.

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Fire ants conquered America by monopolising calorie-rich food

By Ed Yong | December 5, 2011 3:00 pm

They came to America and found a nation overflowing with calories. Carbohydrate-rich fast food was available on every corner, and with little competition for it, the migrants ate their fill. Soon, they started spreading throughout this new land of opportunity. They are red imported fire ants (Solenopsis invicta) and their invasion is well underway.

The fire ant is an international pest. It devastates native ants, shorts out electrical equipment, damages crops, and inflicts painful stings. It hails from Argentina, but it was carried to the United States aboard cargo ships that docked at a port in Alabama. That was in the 1930s; since then, this invader has spread throughout the southern states, from California to Florida. The country spends over a billion dollars every year in attempts to stem the invasion.

Now, Shawn Wilder from Texas A&M University has found that their remarkable invasion has been driven by partnerships with local insects. The fire ants run a protection racket for aphids and other bugs, defending them from other attackers. In return, they get honeydew, a sweet nutritious liquid that the bugs excrete, after they suck the juices of plants. They are both farmers and bodyguards.

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Jellyfish shift ocean food webs by feeding bacteria with mucus and excrement

By Ed Yong | June 6, 2011 3:00 pm

Despite its name, the Gulf of Mexico’s Dead Zone is full with life. This region stretches over 22,000 square kilometres, an area the size of Israel. Its waters are choked by a combination of fertiliser, sewage and industrial run-offs, flowing down from the businesses that line the Mississippi. These pollutants feed large blooms of algae that ultimately rob the water of oxygen, depriving it of the ability to support fish and other typical residents. Instead, the Dead Zone has become the dominion of jellyfish.

Jellyfish congregate here in their thousands. Locals like moon jellies and sea nettles are joined by foreign travellers like the Australian spotted jellyfish. These gelatinous swarms stretch for miles, covering the ocean in a web of pulsating umbrellas and stinging tentacles. At their densest, you could scoop up a hundred jellies within a single cubic metre of water. They shut down beaches, fisheries, industries and ecosystems.

The reasons for these swarms are unclear. By overfishing, we could have removed the jellies’ main competition for food. By sinking man-made debris like vehicles and rigs, we could have created habitats for their larvae. By raising the temperature of the oceans and pumping them with pollutants, we could have created warm, oxygen-poor waters that only they can thrive in.

The jellyfish blooms are a natural phenomenon but marine biologists suspect that they are becoming increasingly common. Reports are constantly flooding in of unusual thick and large swarms, not just in the Gulf of Mexico, but all over the world from the Mediterranean to the Japanese coast. The worry is that we are witnessing a transition from an ocean full of scales, shells and flippers to one that’s ruled by jelly.

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The bees that mummify beetles alive

By Ed Yong | May 30, 2011 9:00 am

In Australia, the penalty for burglary is several years in prison. But that’s for humans. For the small hive beetle, breaking and entering into the hive of stingless bees carries a far harsher sentence – being mummified alive in a sticky tomb of wax, mud and resin.

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Drying out the cane toad invasion

By Ed Yong | February 22, 2011 7:00 pm

In June 1935, the cane toad began its invasion of Australia. Sailors brought the animal over from Hawaii in an attempt to control the cane beetle that was ravaging Australia’s sugar cane crops. It was a mistake that the continent’s wildlife would pay for. The toad did nothing to stop the beetles. Instead, it launched its own invasion, spreading across the continent from its north-eastern point of entry. As it marched, it left plummeting populations of native species in its wake.

The toads are born conquerors. Females can lay 35,000 eggs many times a year, and each can develop into a new frog in less than 10 weeks. They’re unfussy eaters and they’ll munch away on bird eggs, smaller native frogs and more. And they have large glands behind their heads, which secrete a milky poison. Local predators (or domestic pets) that try to eat them tend to die.

Now, Daniel Florance from the University of Sydney has found a clever way of corralling the cane toad invasion. He realised that humans have continued to give the toad a hand, long after we first brought them to Australia. By creating dams and troughs, we provided the toad with watery staging grounds that allowed it to spread across otherwise impassably dry land.

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Invasive shrub increases risk of human disease (via ticks, deer and bacteria)

By Ed Yong | October 11, 2010 3:00 pm

Honeysuckle_deer_tickThere are many ways of fighting disease, but Brian Allan from Washington University has suggested a most unusual one – a spot of weeding. Allan’s research shows that getting rid of a plant called the Amur honeysuckle might be one of the best ways of controlling an emerging human disease called ehrlichiosis. The plant, however, doesn’t cause the disease. The connection between the two is far more complicated than that.

The Amur honeysuckle is an Asian plant that’s naturally alien to American shores. But, like many species that are brought to new habitats, it has become an invader. It forms thick growths that deprive native plants of light, causing local diversity to plummet in the face of an expanding blanket of honeysuckle. This story has been repeated all over the world with different species cast as invasive villains, and different communities cast as suffering victims. But the true consequences of these invasions often go unnoticed.

The honeysuckle doesn’t just crowd out local plants; Allan has found that it also attracts white-tailed deer. Where the deer go, so do their parasites, and these include the lone star tick, the animal that spreads ehrlichiosis. Through their blood-sucking bites, the ticks spread five species of bacteria that infect and kill white blood cells. This weakens the immune systems of their hosts and causing the flu-like symptoms that accompany a bout of ehrlichiosis.

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The stealthy sea walnut sucks to succeed

By Ed Yong | September 20, 2010 3:00 pm

It’s the open ocean. A baby fish, less than a centimetre long, floats through the water, completely oblivious of the danger it is in. It’s caught in a current, but one so smooth that the fish cannot detect it. Its only clue to what’s happening comes too late, as it’s suddenly sucked into a ring of tentacles and swallowed by one of the ocean’s stealthiest predators – the sea walnut.

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