However, get medical help right away if you notice any symptoms of a serious allergic reaction, including: rash, itching/swelling (especially of the face/tongue/throat), severe dizziness, trouble breathing, kidney problems (such as change in the amount of urine). This is not a complete list of possible side effects.
They are more active when it is cooler, but they can and do come out of hiding at any time of the day. Here in the desert, Arizona Rattlesnakes can easily overheat and die if they cannot find a cool place to keep themselves cool.
The largest rattlesnake round-up in the United States is held in Sweetwater, Texas. Held every year since 1958, the event currently attracts approximately 30,000 visitors per year and in 2006 each annual Round-Up was said to result in the capture of 1% of the state's rattlesnake population.