Stephanie Mellom didn't realize she had been bitten by a poisonous spider while she slept.

"I felt a bump on my chest and I thought it was just like a bump you have on your face," she said.

However, when the bump became bigger, painful and red, Mellom went to the doctor. She was experiencing classic symptoms of a brown recluse spider bite.

There are two types of spiders that are dangerous to humans in the U.S.: The brown recluse, known for the violin-shaped mark on its back, and the black widow, indentified by the red hour-glass mark on its belly. The bites from these spiders are rarely fatal, but they can be dangerous.

"The distinguishing factor between a pimple and a spider bite would be pus," said Dr. Keith Jeffords, of Emory University. "Pimples have pus, infections have pus ... ."

Spider bites do not have pus. Doctors say it's the venom that causes serious damage.

"It destroys the skin tissue, the superficial skin tissue, and what you see is it looks like a severe burn almost," said Jeffords.

In addition to a red, itchy, painful bump, a bite from a poisonous spider can also cause fever, nausea, vomiting and sometimes sever abdominal pain.

Medications are available to treat both kinds of spider bites. But it's important to seek help as soon as possible. After six weeks, Mellom was finally feeling better.

Experts say the northern black widow spider is found throughout Michigan's lower peninsula. Brown recluse spiders are more common in the south but have recently been found in mid-Michigan.