The City of Fredericton is warning residents to avoid picking up Hickory Tussock moth caterpillars as the fuzzy, white caterpillar can cause a rash.

The caterpillars have been in New Brunswick for years and can be found eating their way through leaves of oak, hickory, walnut, ash and elm trees, fattening up before they cocoon.

But in the past couple of years, the population has been growing. 

While the caterpillars do not damage the trees, they can damage the skin of anyone who picks them up for a closer look.

Don Murray, the parks and trees manager at the City of Fredericton, said people should be careful to avoid the caterpillars.

"If you let your kids pick them up to play with them, which kids tend to like to do, because they are a very nice little fuzzy caterpillar when they walk across your arm," Murray said.

"They could leave a rash on your arm very similar to poison ivy.  And it can be painful, and it can be itchy."

Entomologists recommend washing the skin with soap and water if they come into contact with the caterpillars.

The itching is caused by a venom the caterpillar excretes. And the black antennae are barbed.

Phil Currie, the owner of Currie’s Greenhouse, had a favourite place to sit outside of his greenhouse until he had an encounter with one of these caterpillars.

"One dropped down and got between my fingers and I didn't realize and I squished it and two days later I had a rash around here, and it itched like the dickens," he said.

When his customers ask for his advice on what to do with the caterpillars, he said he offers some guidance that he admits he feels bad giving.

"Step on them, as fast as you can, just step on them, don't pick them up," he said.