A hand holding a red swamp crayfish.
Red swamp crayfish are getting cosy in Delft. Fabrizio Bensch/Reuters

If you can’t beat invasive species, maybe you can eat them.

The Netherlands is well known for its international atmosphere, but not all new arrivals are welcome. Take, for instance, the red swamp crayfish. No one is happy to welcome it to The Hague.

Crayfish were first sighted there in the early 1980s, but the issue went relatively unnoticed for many years. These crustaceans arrived from Louisiana, and made their way into aquariums or garden ponds. Then they escaped. Now, the region’s crayfish population is considerable: “In Delfland, we’re talking [about] at least millions. You look underwater and grab a net and you see thousands in a square meter,” says Ernst Raaphorst, an ecologist working for the Delftland Water Authority. This sounds like a lot, but Raaphorst puts the numbers in perspective: “The smaller the animals are, the more you need [in order to] take notice of them. There are millions of square meters of fresh water in Delfland, so it quickly starts adding up. It’s still many, but it’s not like they’re everywhere.”

The crayfish poses problems for the city’s waters and the industry that depends on them. Crayfish damage canals by digging into the ditches to hide, to survive the winter, or to lay eggs. But by doing so, they are muddying up the waters, which diminishes the amount of light the plants get. This changes the water quality, as well as the whole ecosystem in it: If there are no plants, there are no fish, either. That’s why in Dutch, the crayfish (and other highly invasive species) are sometimes called ecosystem vormers, or “shapers.”

According to a new European law, the American crayfish is considered an invasive species and therefore can’t be kept, sold, or bred. With current tools, it’s not possible to wipe the species out—and the more extreme measures, such as poison, may cause even more damage to canals and the creatures that live there.

Raaphorst says the problem will likely be tackled on the province level, rather than nationally. However, there still isn’t much information concerning the exact numbers and location of crayfish. The Water Authority asks residents to report crayfish sightings on a special website and on the agency’s Facebook page. The responses have been overwhelming. “It doesn’t tell us [everything]; we didn’t get many accounts from agricultural areas, because there are not many people to see them. It just shows where people are confronted with them,” Raaphorst says. “But we get a better feeling of the current state of affairs.”

In its native Louisiana, the crayfish leaves its usual habitat to colonize new terrain. In the Netherlands, however, it tends to migrate over land even though all canals in the country are connected. Raaphorst suggests that this may be an instinctual behavior that doesn’t make sense in its new habitat. Meanwhile, it leaves the crayfish vulnerable to attacks. Moreover, local parasites and birds have learned to prey on the invader. Even if these other hungry creatures keep the crayfish numbers level, “a stable population could still be very many,” says Raaphorst. Plus, there is nothing preventing the crayfish from moving on to other Dutch cities, and later across the border to other countries.

Catching them isn’t enough. That’s because the crayfish eats fish, plants, and sometimes its own young. Fishermen usually only capture the big ones, which allows the younger ones to grow up. “If you start catching them you might actually increase the population,” Raaphorst says. If controlling the population is too hard to manage, Raaphorst suggests that ecologists look to minimize damages by protecting the ditches.

Meanwhile, some people in The Hague are taking matters into their own hands by catching and eating the critters—after all, in its native Louisiana, the red swamp crayfish is already a delicacy.

Christi Westny-de Roo, a Dutch native who lives in Pijnacker, was excited when she saw the crayfish in Delft. Her husband is originally from Sweden, a country with a rich tradition of eating crayfish (though the Swedes consume a slightly different species—orconectes virilis, or the virile crayfish).

In Sweden, people even have crayfish parties complete with conic hats, bibs, and colorful paper plates. “It’s a big thing there,” Westny-de Roo says. “[It’s] silly that everyone is complaining about them here. People would be super happy in Sweden if they just walked into your garden.”

It wouldn’t take much to persuade Dutch people to eat crayfish. In fact, seafood is very popular here and supermarkets such as Albert Hejn already sell crayfish salad. These invasives could easily be marketed as a cheaper alternative to lobster.

Are these rogue crayfish safe to eat? Raaphorst says that the water quality in the ditches is rigorously checked and monitored. However, he also raises some words of caution. “We don’t know if [the crayfish] can accumulate toxic metals in the body; some animals do that,” he says. “We don’t have a policy of advising people to eat them.” However, the Water Authority can only speak to the quality of water, not the animals and plant species that live in it.

Christi Westny-de Roo is kind enough to share a Swedish recipe: Boiled in salt, sugar, brown beer, and the flowers of a dill plant. “And of course, there is some strong schnapps, some beer, and a side of bread and cheese, so it becomes a whole meal,” she explains. If you can’t get rid of the problem, at least you can turn it into a feast.

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