[header] How to kill a venomous spider [title] Spot black widows by their red hourglass mark. [step] If you see a black spider in or near your home that has a bright red hourglass marking on its abdomen, you've spotted a black widow spider. These are extremely dangerous and are potentially fatally venomous. 
Be extra careful around the outside of your home if you live in a temperate climate and have woodpiles; black widows are most frequently found there. [title] Look out for brown recluses' violin-like mark.