GREENFIELD — Local police had a slithery surprise on Thursday morning when they encountered what they believe to be an endangered snake on Pleasant Street.

Greenfield Police Officer Marcus Johansson responded to a report of a large black snake sunning on the side of the roadway on Pleasant Street. He said the caller feared it was a loose pet.

After sending photos of the reptile to the Environmental Police, Johansson said officers believed it was an Eastern rat snake, the longest snake in Massachusetts that is listed as an endangered species.

According to MassWildlife’s Connecticut Valley District Office Manager Joseph Rogers, the rat snake is a particularly rare species in the region.

“As with most snakes in our region, a lot of the issues that they have with populations is really a loss of their habitats, specifically their wintering locations,” Rogers said. “That really limits how many we have on the landscape.”

After learning that the snake was, in fact, not a pet, Johansson drove the snake out to the rocks beside Poet’s Seat Tower, where he released it in a sun-filled spot farther away from a roadway.

Although local police believe the reptile was an Eastern rat snake, Rogers said MassWildlife has not yet been able to identify its species based on the photos the agency received from the Greenfield Police Department.

Rogers added that as cold-blooded creatures, snakes are often attracted to warm surfaces such as rocks or roads, causing them to be hit by vehicles frequently.

“Rat snakes are a fairly rare species across the state, so they are not a commonly cited species. There are a couple of other snakes that can look similar to the species,” Rogers said. “People are becoming more aware of these sightings, and they are reaching out and contacting us. This year we’ve received a few more calls than in prior years, but the number of snakes across the landscape has remained fairly stable.”

Anthony Cammalleri can be reached at acammalleri@recorder.com or 413-930-4429.