Southern Pacific Rattlesnake - Crotalus oreganus helleri

Rattlesnakes are important members of the natural community. They will not attack, but if disturbed or cornered, they will defend themselves. Reasonable watchfulness should be sufficient to avoid snakebite. Give them distance and respect.

"Rattlesnakes are also among the most reasonable forms of dangerous wildlife: their first line of defense is to remain motionless; if you surprise them or cut off their retreat, they offer an audio warning; if you get too close, they head for cover. Venom is intended for prey so they're reluctant to bite, and 25 to 50 percent of all bites are dry - no venom is injected."
Leslie Anthony. Snakebit: Confessions of a Herpetologist. Greystone Books, 2008.

Rattlesnake bites can be extremely dangerous, but rattlesnakes should not be considered vicious and aggressive. They are often called aggressive in movies and stories, but they will not attack without a reason. The image of a rattlesnake we often see in pictures and film, with the body partly coiled, the tail rattling loudly, and the head up ready to strike, is a defensive stance some rattlesnakes use when they sense that crawling away would put them in danger of an attack. This display is a warning not to come any closer or they will strike. If they are given some space and some time to escape to a safe place, they will do so quickly.

Because they cannot move very quickly rattlesnakes often use their cryptic color and pattern to blend into their surroundings to hide from their prey and from other animals that could threaten them. When threatened, they often lie still to avoid detection and do not rattle, because that would give away their location. At other times they rattle loudly, sometimes from a good distance, to warn potential enemies of their presence. In both cases they are doing everything they can to avoid confrontation and to avoid striking and biting and using up their valuable supply of venom which they need to kill and digest their food.