And these signs will accompany those who believe:
by using my name they will cast out demons;
they will speak in new tongues;
they will pick up snakes in their hands,
and if they drink any deadly thing,
it will not hurt them
(Mark 16: 17-18)
The practice began in the 1920s, primarily in Appalachian coal camps. Coal camps at that time were difficult places to be. Shifts were long, typically 12 hours, and the workers were poorly paid. Boys as young as 10 or 12 would join their fathers in the mines to help make ends meet. Workers were kept in line by living in company-owned houses and being paid in script. The script could be used to buy the miners' supplies, food, and clothing at the company store, which sold goods at inflated prices. If nearby businesses accepted script at all, it was heavily discounted. Workers who protested could be fired and immediately evicted from their homes. Families faced the same fate if the miner husband/father was killed or maimed in a mine accident. Salvation to a better eternal life was important, and if "taking up the serpent" was needed to demonstrate one's faith, then so be it.
The best treatment of snake handling in churches that I've seen was Dennis Covington's 1995 non-fiction best-seller, Salvation on Sand Mountain. Covington was a reporter for a Birmingham newspaper when he heard of an attempted-murder trial to be held in Scottsboro, Alabama. A pentecostal preacher from rural Sand Mountain was accused of trying to kill his wife by forcing her to put her hand into a cage filled with rattlesnakes. She was bitten several times, but managed to make it to the road and flag down a passing car. Covington wrote of the trial and his followup visits with snake handlers in several states. The book is still available and I highly recommend it.
This video gives a light view of the practice. Wendy Bagwell and the Sunliters were a gospel music group. Bagwell told stories between numbers and this one became a hit on radio in the early '70s. I still have a 45 rpm recording of it. Enjoy!