It's a jungle down there.

Animals have delayed almost 700 trains in the subway in the past year and a half, according to transit documents obtained by amNewYork.

A frightened gray puppy who snagged 18 L trains in Brooklyn and a lucky cat rescued by a quick-thinking No. 6 train operator in Manhattan were among the 79 incidents reviewed since January 2014.

"We encounter animal incidents from runaway pets to wild animals that can disrupt service," said one transit source. "It can feel like a pet store sometimes because of the number of cute animals walking on the tracks."

The MTA first spotted the gray puppy on the tracks at the Wilson Avenue stop in Bushwick on the afternoon of Jan. 11 last year. The motorman stopped the L train to rescue the puppy, but it eluded capture and ran north.

Eighteen trains in both directions were late because the dog ran back and forth between the Myrtle Avenue and Broadway Junction stations. An NYPD lieutenant eventually rescued the four-legged rail trespasser and took the frisky pup into police custody about 80 minutes later, documents show.

Animals can only be brought onto the train if they're in a container and "carried in a manner which would not annoy other passengers," the MTA rules say.

Pets must be kept in carriers unless they are service pets or working with law enforcement.

"Animals in the system is just one of the countless and uncontrollable elements we face on a regular basis that can impact service delivery," said MTA spokesman Kevin Ortiz.

A mischievous pup's rail antics also led to southbound Q and B trains being rerouted along the N line in June last year while the MTA tried to save it when it was spotted on the tracks at the Newkirk Plaza station. The platform at the station is very low -- and the rogue puppy returned to its owner about 50 minutes later, an internal document shows.

A cat on Manhattan subway tracks was an easier capture but still impacted service on the No. 4 and 6 lines in the morning of May 9 this year. The train operator spotted the feline at the 125th Street station in East Harlem -- and downtown trains were briefly held between Hunts Point Avenue and Third Avenue-138th Street in the Bronx. Luckily, the compassionate motorman rescued the cat from the rails within only a couple of minutes -- preventing any service snags before rush-hour.

Other animals, meanwhile, worsened riders' commutes from inside subway cars. Two Manhattan-bound No. 4 trains were delayed early Feb. 2 morning this year when a leashed bulldog frightened other straphangers. Cops intervened and removed both the intimidating dog and its owner from Brooklyn's Atlantic Avenue-Barclays Center station.

Some animal-loving but reckless subway riders also have risked their lives for animals, video shows. One YouTube video reveals a man rescuing a tiny brown cat from the tracks in the Bronx in January. The straphanger first brings the meowing kitty to safety onto the platform -- then struggles to hoist himself back onto the platform before finally clearing it.

Some loose animals wrecked commutes and then disappeared. Almost 50 trains were delayed this year by a small dog that jumped onto the tracks at Van Siclen Avenue in Brooklyn before it disappeared somewhere south of Euclid Avenue, transit sources said.

Raccoons and opossums also sometimes hang out on the rails -- but at their peril. In May this year, a Q train struck a raccoon at the Beverly Road station while another raccoon on the platform cried, documents also show.

A live opossum litter was discovered alongside its deceased mom at the Metropolitan Avenue terminal on May 19 this year. A transit worker moved the litter and the mother's body to a safe area. Animal Care and Control then took the opossums out of the subway system.

Sometimes subway riders can even be more sympathetic to a four-legged creature on the tracks than they are for a sick human passenger, social media illustrates.

"There's a dog on the train tracks, I hope it's ok," tweeted concerned straphanger @shepotle.

Riders applauded when a black cat was rescued by two transit cops from the Canal Street tracks on July 22 -- even though the wayward kitty disrupted the service of over 80 trains. Furry trespassers also gained celebrity in the summer of 2013 when two adorable kittens played on Brooklyn tracks and halted Q train service.