How it kills: These diamondbacks aren't known for being the most aggressive rattlers on the block, but at up to 7 feet long, they're certainly the biggest—and the most venomous in the US, with bites that cause spontaneous bleeding, hypotension, and swelling that can lead to cardiac arrest. When threatened, they can strike a distance at least a third of their length and sink their fangs into your flesh repeatedly, often without rattling to give you fair warning to run. And how are they threatened? Well, say, when you bump into them in your own house!
How to get it before it gets you: Unfortunately, your basement or garage may be more welcoming than any burrow or nook outdoors, especially when it's hot and muggy. Seal all foundation cracks and any openings ¼ inch or larger. Close the garage door when it's unattended, and be careful when accessing crawl spaces. Keep your yard tidy so snakes have nowhere to hide.