Redbacks usually prey on insects but they can capture larger animals that become entangled in the web including king crickets, trapdoor Spiders, and small lizards.
It can just be a red back spider...
a wolf spider. they hurt but are not deadly to humans
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.
It is a type of house spider, likes dark places like cellers, attics e.c.t... And will eat any type spider if it is hungry, and will also eat its own kind if no food is found hope that answers your question.
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