What markings do red back spider have?

An female, adult redback is black/brown with a red striped down her back. Sometimes this may have breaks or be uneven, but not usually. She also will have an "hourglass" marking on her underside, like the black widow (they are closely related).

A juvenile female is black/brown and has the same markings, although the stripe may be broken (or even missing if she is very young!) and will often have a white outline around the stripe. Sometimes she will have white stripes on her legs.

A male is brown, inconspicuous and tiny, sometimes with some faint stripes.

The best way to find out is just do a google image search for "female redback spider"