Memorial Day revelers who flock to the Jersey Shore are being advised to be wary of a real sting operation.

Hundreds of unwelcome visitors – toxic jellyfish noted for their tiny size and excruciating sting – have been spotted in recent days by researchers in Barnegat Bay, according to reports.

The latest count of almost 300 of the spineless creatures has the head of the Marine Biology and Coastal Sciences Program at Montclair State University convinced that tens of thousands them are living in areas of the bay.

“When we’re finding hundreds, or 500 of these, it really means that there are thousands and tens of thousands of polyps (or baby jellyfish) … out in the local waterways,” Paul Bologna told the Asbury Park Press.

The clinging jellyfish have intense stings that feel like “a whole body charley horse,” he said.

While the pain of other jellyfish stings usually decrease with the passage of time, the pain of these dime-sized jellies can increase with time and leave a person writhing in agony, Bologna warned.

“They have two sets of venom that are really problematic,” he said. “The first is paralysis and the second is a neurotoxin.”

Each transparent jellyfish features between 60 and 90 stinging tentacles, according to the New Jersey Department of Environmental Protection.

Their stings are so painful that two men were hospitalized last summer on morphine drips after swimming among the jellyfish in Barnegat Bay.

Bologna said the samples — mostly taken along the Metedeconk River and northern Barnegat Bay along the coast of Ocean County — showed higher numbers of these specimens than were found in previous years.

This story originally appeared in the New York Post.