They're wrinkly and rare, and the biggest ones can grow up to 2.5 feet long.

Missouri's population of endangered hellbender salamanders recently got another huge boost from the St. Louis Zoo, Missouri Department of Conservation and U.S. Fish & Wildlife Service to help them survive in the wild.

After hatching and raising a bunch of hellbenders at the zoo, more than 1,000 of the slippery salamanders were released into Ozarks streams and rivers in southern Missouri that provide suitable habitat for them.

They'll seek out submerged flat rocks to hide under and ambush their prey of fish, crayfish and small invertebrates.

They also, hopefully, will breed new generations of wild hellbenders. Since 2008, and including the most recent effort, MDC and the zoo have teamed up to raise and release more than 8,600 hellbenders into Missouri waters.

"We want them to join the wild hellbender population," said Lauren Augustine, curator of herpetology at the St. Louis Zoo. "All are tagged before they're released, and MDC does surveys to see how they are doing."

Neither the zoo nor MDC would say where exactly the hellbenders were set free. There's a reason for that.

They're trying to prevent unscrupulous wildlife poachers from catching and selling hellbenders to people who want a rare, endangered and exotic pet.

"Some people want to have rare and unique species in their collection," Augustine said. "It has been an issue. That's why we keep their release sites so secret."

For the record, it's a crime to catch and sell hellbenders.

According to the Missouri Department of Conservation, hellbenders are the official endangered species of Missouri and the largest aquatic salamanders in North America.

Missouri is the only state that has both subspecies — the Ozark hellbender and the eastern hellbender.

A population assessment showed all hellbender populations have an above 96 percent risk of extinction over the next 75 years unless the population increases.

According to the U.S. Fish and Wildlife Service, both the Ozark and eastern hellbender populations in Missouri have declined more than 70 percent over the past 40 years.

To slow endangerment of the amphibians, the Saint Louis Zoo began raising hellbenders from eggs.

The zoo houses facilities to simulate the habitat of hellbender breeding groups. The facilities include two 40-by-6-foot outdoor streams with natural gravel, large rocks for hiding, and artificial nest boxes for egg-laying.

Every year, hellbenders are released to native Ozarks rivers based on when they were hatched.

MDC State Herpetologist Jeff Briggler says the process of releasing the hellbenders was different this year due to the pandemic.

“The restoration team’s priority was to reduce contact and maintain social distancing among individuals,” Briggler said. “To achieve this, animal transfers from the zoo staff to the state herpetologist occurred in open-air parking lots.”

Briggler said crews who released hellbenders were reduced and limited to two individuals per boat.

MDC says in addition to breeding efforts, the zoo has also been head-starting juvenile Ozark and eastern hellbenders, hatched from eggs collected in the wild, for future release.

Once the captive-bred larvae are two to eight years old, they can then be released into their natural habitat — the Ozark aquatic ecosystem.

Missouri Department of Conservation biologists are monitoring the success of these released animals in the wild.

In 2001, the Ozark Hellbender Working Group of representatives from state and federal government agencies, public universities and zoos in Missouri and Arkansas launched a number of projects to combat the Ozark hellbender’s decline.

These included egg searches, disease sampling and behavioral studies, to name a few. In 2004, funding from private donors, MDC, USFWS and the zoo covered the cost of building sophisticated facilities, including climate-controlled streams to breed the hellbender.

Collection of the zoo-bred stock and eggs for propagation efforts at the zoo was done by MDC biologists. 

"Snot otters"

Also known by the colloquial names of "snot otter" and "old lasagna sides," the adult hellbender is one of the largest species of salamanders in North America, with its closest relatives being the giant salamanders of China and Japan.

It has a restricted range and is only found in the cold-water rivers of south-central Missouri and adjacent north-central Arkansas. Hellbenders have broad, flat heads, small lidless eyes and pronounced skin folds on the sides of their body.

They can live for more than 25 years on a diet of crayfish, fish, worms and snails. Large rocks on the river bottom provide refuge and nesting sites.

In late summer and early fall, a male hellbender establishes a nest site under a large rock or within a rocky crevice and waits for a female to enter and deposit her eggs to be fertilized. The male defends its nest until the eggs hatch and resulting larvae depart the nest chamber months later. 

Anglers using crayfish, worms or small minnows might occasionally catch a hellbender. Anyone who hooks a hellbender should remove the hook as gently as possible and immediately release the salamander back into the water.