The U.S. Fish and Wildlife Service is proposing strict nationwide limits on importing and shipping boa constrictors and four other snake species.

The rules would prohibit bringing the snakes into the country and shipping them between states except for scientific and educational purposes. The agency wants to prevent them from being introduced into the wild.

The other species are reticulated python, green anaconda, Beni anaconda and DeSchauensee's anaconda.

The agency says most of the snakes enter the U.S. as pets. Many are released by owners when they grow too big, and other pet snakes escape from inadequately secured pens.

Importing snakes is already illegal in Hawaii.

Christy Martin, spokeswoman for the Hawaii Coordinating Group on Alien Pest Species, says federal rules would further discourage people from bringing snakes to the islands.