Luckily they have a red hourglass on their underside, which is made visible by the female's habit of hanging upside down from her web. Black widow populations are erratic, sometimes rising and falling dramatically over the years. They prefer to make their webs in dark, dry, undisturbed places. They are common underneath houses, in garages, or outside in woodpiles. Black widow webs are very irregular in design, not looking like the traditional bulls eye shape.
Females can get defensive around their webs and bite, especially when there are egg sacs present.
The venomous bite from one of these spiders causes pain rather quickly. If a black widow bite is suspected, look for the two small teeth marks on the swollen area. Watch out for signs like nausea, tremors, and sweating if bitten. First aid such as washing the area and applying ice can provide minor relief. To keep from getting bitten wear gloves when working in areas that could have spiders, and pay attention.