Err...it's actually a sign of discomfort, not something they do for fun. It can mean worms, or it can also mean they have swollen glands in their rectum that cause them irritation.

very seldom worms, that's more of a very common myth. Worms don't usually cause itchyness/irritation of the anus, although it is possible with tapeworms. Not usually seen with Hook worms / round worms / whip worms or other common parasites.

This is most often a sign of impacted anal glands, as you mentioned. It can also be caused by other things that cause general itchyness such as fleas biting around the rear end, skin allergies, and so on.

Most often cause though is anal glands.

Anal Glands, in most dogs, are emptied on their own every time the dogs use the bathroom. Some dogs however, especially smaller breeds, have issues with them. Usually it's because the anal gland liquid is too thick and doesn't express on it's own, or it could be due to an infection of the gland itself.

Either way, a vet trip is in order. If you think it might be a recurring problem in your pet, it would be cheaper to ask your vet to teach you how to empty the glands yourself. It's not a fun job, but can be necessary, especially if you don't want to pay for a vet visit every couple of months.

As for me, well, it's my job to empty them out on a daily basis. I'm a vet tech :P

*nods* Though my only nit pick would be getting your vet to show you how to do it.... Some dogs that's fine (the smaller ones) but if a large dog needs them expressed or a small one has a sever case then it would be a trip to the vet. It would have to be expressed internally... none of it's fun.

(I've been fortunate not to have to do it yet, but we do them in grooming if they need doing.)

If your got kids make shore they have good teeth and health... If you have pets do the same eh, I got two big med kits in my home... Infact you could say a full shelf and I can see some things are nasty to do.. Like ripping on those gloves and just doing it. goes with any thing like if some one is bleeding from a main blood flow don't go ewwww yuck, get that thing at the end of your arm and help them. Guess its really about, Do you have that internal switch in your head.. "Vet, Doc, Nurse, Paramedic, First Aid'er they know it"

It could also mean tapeworm or any other number of parasites. But many dogs also do it for pure fun! ^_^ *is in animal care program studying this right now* But thank you for the comment

We have four dogs but luckily only one of them really does this. She is healthy though.