Which tiny insect can bite and irritate a dog or a cat so much that they constantly scratch themselves?

Explanation

A flea is a small wingless insect that lives as a parasite by sucking the blood of mammals and birds. There are different species of fleas including bird, cat, dog, human and rat fleas. The fleas lay eggs that develop into larvae, pupae and then adult fleas. Adult dog fleas feed on the blood of dogs and cats and occasionally bite humans.