The herpetarium staff at Gladys Porter Zoo announced Wednesday they successfully hatched six Mangshan vipers. 

The Brownsville zoo is the third institution in the U.S. to successfully breed and hatch the rare species. 

Staff says they've been working with the species for 12 years. 

There are fewer than 500 left in the entire world, so any animal bred in captivity is a plus for conservation status. 

The babies will not be in the exhibit for a while, but the parents are still on display.