While they aren't very big (female black widows only get to be about ½ inch), black widows strike fear in the hearts of many homeowners. Characterized by their jet-black bodies and distinctive red markings with the female typically displaying a red hourglass mark. In homes, they can be found building webs under desks and other furniture. If you are unlucky enough to be bitten by one of these spiders, seek immediate medical attention, as their venom has systemic effects on the body like muscle spasms and abdominal cramps.