Eight tentacled snakes were born at the Smithsonian’s National Zoo last month, surprising zookeepers who had spent four years trying to breed the reptile.

The snakes, which can grow up to four feet long, have venom designed to strike different prey in different way. They are aquatic ambush hunters, officials said. Under cover of night, they stay motionless underwater. But when they sense victims, they strike to kill.

Breeding the snakes at the zoo, and seeing them survive after birth, has proved difficult, however. The Oct. 21 birth marked the first time in 11 years that any tentacled snake at the zoo has given birth to offspring able to survive outside the womb.

“It could be that they were relatively young before,” reptile discovery center keeper Matt Evans said of the snakes’ inability to give birth. “Even though they looked like they were pregnant this time, we weren’t expecting anything different.”

The reptiles, native to Southeast Asian lakes and rice paddies, resemble a cross between a slug and a snake, with two tentacles protruding from their snouts.

“They look super cute, super small,” Evans said. “They’re incredibly neat just because of the adaptations they have to live in a murky environment.”

When hunting, they anchor themselves underwater with their tail and wait for prey, using their tentacles to detect vibrations from passing fish. Though venomous to prey, tentacled snakes are harmless to humans.

“Within a few hours of being born, the snakes were already acting like adults,” Evans said in news release. “Instincts took over and they were hunting. We don’t know much about this cryptic species, but we’re already learning so much just watching them grow.”

The baby snakes were briefly on exhibit after birth but are now being privately cared for and fed. Once keepers are sure the snakes are eating and growing properly Evans said they will be put back on exhibit for the public.

The National Zoo is one of only a few in the country to host the species, according to zoo officials. The Zoo’s four adult snakes are part of a permanent exhibit at the Reptile Discovery Center. The newborn snakes will likely be sent to other zoos.