The dog's got fleas but the cat hasn't - why?

In a sense you're lucky, if one of your pets is reasonably resistant to fleas, but I'd like to answer the question by framing it in a completely different way.

The dog's got flea's, so I'm assuming that you are trying to get rid of them with a reliable flea treatment. But are you treating your cat?

Many pet owners assume that they only need to treat their animals which are definitely carrying fleas. But some animals don't necessarily have as many fleas as another. This can particularly affect cats who, because of their grooming habits, may tend to either swallow or injury many more fleas than a dog would. So on a quick examination your cat may not appear to be carrying any fleas. And here's the rub - it's not whether you cat appears to have fleas that's important, it's whether he or she actually does. I think that any one of your pets has fleas, you can guarantee that other animals in the household do - even if you've not yet spotted them.

So now to answer your question. If you are treating all of your animals, then the dogs got fleas because they are easier to see on dogs. If you are treating your dog but not your cat, then the answer to the question we posed first is your cat DOES have fleas but you can't see them. Remember, every adult female flea lays around 20 eggs per day. So, if you aren't finding the 2-3 fleas that are on your cat, these fleas are still contributing 40-60 flea eggs into your home environment every day - that's where the fleas you are seeing on your dog are coming from.

So the moral of the story is simple - all animals in a household must be protected by an effective flea treatment, even if you've never seen a single flea on one of them.

IF THERE IS NO CONTACT WITH FLEAS THERE ARE NO DEAD FLEAS!

In other words - don't be bothered if you see fleas on your pet.

Only be bothered if it is clear they are not being killed.

Fleas which are being killed are slow and easier to catch than their non-affected cousins. And fleas take some hours to die after jumping on your pet - in spite of some of the advertising material out there.

So relax - you pet still has fleas - you are in good company - just check that your flea treatment product is killing them.