a wolf spider. they hurt but are not deadly to humans
Black and red spider
It can just be a red back spider...
A spider.
The spider that is black with a white crescent on its back is the Brown House Spider. This spider is often confused with the red-back spider.
a red back.
red back spider
A black widow spider is black with a red mark on it's abdomen; this might or might not be what you meant. The black widow sometimes has a red mark on her back, as well. The red backed spider of Australia, a relative of the black widow, has an orange red mark on the back.
a spider.
red back
Arachnic
Have seen a very small spider with 4 white dots and 1 red dot. Not a red back. Ta ~Snaff
A green spider with a red spot is dangerous if it is a red back. Normally, green spiders are not dangerous.
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.