All spiders have poisons - most are harmless - but one of the most severe is in the Black Widow, Dr. Walker says. “The skin around a bite from a black widow will often turn red, with a central white area,” Levine adds. The venomous spiders hide in wood piles and tree stumps. Some bites are painless and others can cause sharp pain. Look for one or two red incisor marks at the bite site.