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Israel Nature and Parks Authority inspectors went on high alert recently following the sighting of evidence that one of the worst invaders in the animal world - the red swamp crayfish - could be proliferating here. A researcher from Tel Aviv University chanced upon the crayfish in pools of water near Hadera and notified the authority, which plans to trap the invaders and prevent them from spreading to areas where they could cause serious harm to all local ecosystems.

Gil Wizen, of Tel Aviv University, visited the quarry sites on the outskirts of Hadera last spring to study the pools of water there, as part of a research project on beetles. "I found molts (exoskeletons) that the crayfish had sloughed off as they grew," recalls Wizen. "I realized that these molts were from a crayfish species that is not indigenous to fresh water ponds in Israel."

Wizen embarked on a systematic survey of more ponds and discovered dozens of crayfish. He collected some of them and took them to Prof. Avital Gazit, of the zoology department at TAU, and to Prof. Bella Galil of the Israel Oceanographic & Limnological Research Institute. The creatures were identified as red marsh crayfish, and the survey's findings were recently published in the scientific journal Aquatic Invasions.

The crayfish, which originate in the southeastern United States, are infamous around the world for the damage they do.

"This is a crayfish species that is sold all over the world for food and as an aquarium pet," says Wizen. "In many places the crayfish are set free or escape and immediately start spreading and multiplying."

This unwanted visitor, which can grow to a length of 20 centimeters, can endure dry climate conditions and environmental pollution. Crayfish burrow under the ponds and can survive long after ponds have dried up over the winter and crawl over dry land from one pond to the next. "It eats everything," says Wizen, "including amphibian eggs and tadpoles. In Europe red swamp crayfish have completely taken over the habitats of local crayfish species, and the plants it eats cause the destruction of the food sources and breeding sites of other wildlife."

The most dramatic evidence of the impressive success of unwanted crayfish is in Egypt. About 30 years ago an Egyptian shrimp farmer freed crayfish into the Nile, and since then these invaders have spread 500 kilometers along the length of the river.

"I have no idea how the crayfish found their way to the ponds near Hadera," says Wizen. "We know that they are marketed and raised in Israel. Perhaps one of the breeders wanted to get rid of his crayfish and freed them into the ponds. Or maybe someone freed the crayfish in the hope they would multiply and he would be able to capture them later." The findings of the research at the Hadera ponds was quickly relayed to Nature and Parks Authority officials, with a recommendation to eradicate the crayfish population, but not by poisoning them, as this would contaminate the ground water or harm other wildlife.

"We started to spread traps near the ponds, but since the crayfish were not active during that season, we only caught a few," says Dr. Yehoshua Shkedi, director of the science division at the Nature and Parks Authority. "We will try again in the spring, and, if we are unsuccessful, we will reconsider using pesticides or covering the ponds with dirt and burying the crayfish. Anyone who owns pets should realize that they must not be set free, because they can do tremendous damage."