An invasion of giant purple slugs are washing ashore in the East Bay, populating beaches and waterways.

Experts say the high volume of these slugs may be caused by warmer temperatures near coastal waters.

The slugs themselves are harmless herbivores, but their enormous size and slimy abundance is disturbing beach-goers.

“We are getting calls from the public asking what the heck is this big weird purple blob,” said Carolyn Jones, a spokeswoman for the East Bay Regional Park District. “It’s native to our area. It’s not endangered, but they are rarely seen other than an occasional one here or there.”

While the quantity of washed-up slugs hasn’t been enumerated, dozens at a time have been seen on the shores. The slugs were also spotted last month in an inlet leading to Lake Merritt.

The slugs can grow to be up to 15 pounds, and more than 30 inches in length, according to officials.

Morgan Dill, a naturalist at the Crab Cove Visitor Center in Alameda. “We can’t say for sure why we’re seeing so many, but the Bay temperatures are definitely warmer this year,” Dill told AP.

In Oakland, local resident Joel Peter said “I had never seen one before, and then all of a sudden there were 22 of them with these brilliant colors,” Peter said. “They really caught my eye.”