is it a tarantula? if so, it's a Mexican redknee tarantula.
http://www.Google.com/search?hl=en&q=Mexican+red+knee+tarantula&btnG=Google+Search
spider man (earlier idiot answer)
(my answer) its a Mexican red-knee turantula
There are two that I know of with red backs,
1. The black Widow
2. The Red Backed jumping spider
Red backed jumping spider
black widow spider
black widow
A black spider with a red back and thick fuzzy legs is commonly called a jumping spider. The formal name is Phiddipus audax.
A black widow
tarantula
http://en.wikipedia.org/wiki/Redback_spider
that sounds very possibly like a mouse spider
it iz a black woodow
A black spider that has a red stripe on the back is possibly a red spotted ant mimic spider. They walk on six legs instead of eight and can be found in Arizona.
you have found aRED BACK SPIDER! watch out. poisonous
A ladybird spider is a spider whose red body has four black dots.Specifically, the spider in question can be found natively in Greece. It carries the scientific names Eresus cinnaberinus and E. sandaliatus. It has white-striped black legs. Its fused head and thorax (prosoma) is black. Its abdomen-like rear (opisthosoma) is red, with 4 black dots.
black widow, if it bites it WILL kill you
a black spider
You can make Halloween spider legs out of black pipe cleaners for small decorations. Halloween costume spider legs can be made of black material or black tights.