TUCSON, Ariz. (CBS) — Pool owners in Tucson are dealing with a caterpillar infestation.

Thousands of the crawlers are plugging pools in one of the city’s neighborhoods.

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A local expert says the creatures are harmless.

They’re called white-lined sphinx caterpillars and they can take over entire backyards.

A pool cleaner says he’s never seen anything like it before.

“There were just way too many to count,” said the pool cleaner. “I’ve never seen anything to this magnitude. I mean, it’s just unbelievable how many there are and how many we’ve pulled.”

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The caterpillars are looking for holes to dig, but they keep ending up in pools, instead.

The ones that survive will turn into moths.