You're a very lucky man to still have your arm, and yes, getting bit by one of these critters can make you check your clothes and shoes to prevent further problems.
I am an RN and conventional medicine was unable to treat my brown recluse bite, and so I found an old native Hopi recipe that includes making a poultice of the following in equal parts:
mix this poultice with a little olive oil, and apply to wound 3-4 times daily. This simple little poultice started working right away, stopped the spread of the necrosis and saved me from having to have my foot amputated .... just thought I'd pass this little recipe along