Albion Monitor /Features
 Alien Invaders: Insects interrupt the food chain

Flotilla of Fleas

by Elaine Hopkins

The entire ecosystem of the rivers and lakes could be affected

Quietly, invisibly, a tiny invading army has drifted up the Mississippi River and into the Illinois River enroute to a prized destination: the Great Lakes.

Not the first invader to take this route, and probably not the last, this newest outsider penetrating the North American waterways is a one-eyed water flea, barely a quarter of an inch long. But its arrival has set off concern among scientists working at the Illinois Natural History Survey's field station at Havana, Illinois.

The creature carries the potential to displace native water fleas, a type of plankton or algae, said agency scientist Jim Stoeckel. And if that happens, the entire ecosystem of the rivers and lakes could be affected, as larval fish lose a food source and starve in infancy.

The invader is native to regions of Africa, Asia and Australia. It's bigger than native water fleas and different. Stoeckel described it as a "giant pincushion," compared with other water fleas.

"One long spine protrudes from the head, another from the tail end. Smaller spines cover the body," he wrote, in a paper first published on the agency's home page on the Internet.

Known by its scientific name of daphnia lumholtzi, the invader was found last year as far up river as Henry and Hennepin in Illinois. "That's the northernmost population that's been detected so far," said Stoeckel. "We're on the fringe of this advance. How far north they're going to expand we don't know yet."

The new invader joins many other exotic species entering North American waterways from elsewhere

Like native water fleas, the spiny invader sits near the bottom of the river food chain. Larval fish rely on water fleas for their food source until they grow big enough to feast on other items. Eventually they grow into game fish prized by anglers, eagles, and other creatures at the top of the food chain.

But first these tasty fish must survive the larval stage, and that survival depends on the food supply, Stoeckel said.

If the invasive water flea begins to replace native water fleas, the larval fish could starve, the scientists believe. That's because the invader's size and spines rule it out as lunch for a larval fish. So the invader may have no natural enemies to check its population.

"In a worst-case scenario, this could result in a decrease in numbers of sport and food fish," Stoeckel wrote.

Another agency scientist, Doug Blodgett, said so little is known about this creature that it doesn't even have a nickname. It won't be called "spiny," he said. A native water flea is already known as the spiny water flea.

Blodgett was not sure whether any river dwellers would eat the prickly invader. If the spines drive predators away, the critter has a survival advantage, he said.

"They could become the predominate species," said Stoeckel. "They could outcompete the natives."

Scientists also do not know the range of water temperatures the invader can withstand, said Stoeckel, but no one wants it colonizing the Great Lakes. Even though Lake Michigan could prove too cold, Lake Erie is warmer and might provide a suitable habitat, with subsequent impact on fish, he said.

The invading water flea can be seen by the human eye, but its tiny size and lack of pigment make viewing difficult. Though ugly, it's apparently harmless to humans, Stoeckel said, and would harmlessly pass through anyone unwittingly gulping a mouthful of river water.

The new invader joins many other exotic species entering North American waterways from elsewhere, he said, including the zebra mussel. At least this invading water flea hasn't threatened to shut down power plants, or carpeted its newly acquired territory. Yet.

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Albion Monitor March 10, 1996 (

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