my poor girl - all red and baldy

[DionneUK]

I was stroking my bitch yesterday and noticed she had bald patches on her back. It is completely bald where her fur should be and the bald patch is about the size of a tennis ball. It is a little bit red too. Is it fleas where she has been scratching and gnawing? I don't have a clue what it is. I have a male too but he appears fine and his fur is all intact.

it would have to be a prety bad case of fleas to get this bad. have you noticed any fleas, they are easier to see round the ears and head.
it could be mange(sp), which is also an insect which affects the hair and skin. a skin scrape by a vet will tell you if it is or not.
could just be an irritation to something, like have you put shake and vac down or something in the garden.
i would take her to the vet cause mange or fleas it will only get worse. and if it is red your dog is going to be in some pain or discomfort.

could be ringworm?

Could be mange or ringworm. Take her to the vet.