Fleas are wingless, with mouthparts adapted for piercing skin and sucking blood. They live by sucking the blood of mammals and birds. The most common are cat, dog and human.

Cat Fleas are small sucking insects that are about 1/16-1/8 inches long and dark brown. The cat flea, and all other fleas, are compressed laterally, resulting in an extremely thin insect that can be quite hard to find in an animal’s coat. Their back legs are modified for jumping. The cat flea is the most common flea species.

The primary host is the domestic cat, but it is also the primary flea infesting dogs in most of the world. Humans can be bitten, but a long-term infestation of cat fleas cannot be sustained on people. However, if the female flea is allowed to feed for 12 consecutive hours on a human, it can lay viable eggs.

Dog fleas are a species of flea that lives on many types of mammal, particularly the domestic dog and cat. It closely resembles the cat flea, which can live on a wider range of animals and is generally more prevalent worldwide.[1]

The dog flea is troublesome because it can spread flea tapeworms.

Although they feed on the blood of dogs and cats, they sometimes bite humans. They can live without food for several months, but females must have a blood meal before they can produce eggs. They can deliver about 4000 eggs on the host’s fur.

Human fleas, in spite of the common name, have a lot of hosts. they can be found on dogs, cats and other domestic animals, as well as on wild animals.

The adults are roughly 1.5 to 4 mm in length and are laterally flattened. They are dark brown in color, are wingless, have a rounded head and have piercing-sucking mouthparts that aid in feeding on the host’s blood. Most fleas are distributed in the egg, larval, or pupal stages.

Fleas are a pest species to their hosts, causing an itching sensation that results in discomfort and leads to scratching of the bite. Flea bites generally cause the skin to raise, swell, and itch. The bite site has a single puncture point in the center. Bites often appear in clusters or small rows and can stay inflamed for up to several weeks.

Fleas can spread rapidly and move between areas to include eyebrows, eyelashes, and pubic regions. Hair loss as a result of itching is common, especially in wild and domestic animals. Anemia is also possible in extreme cases of high-volume infestations.

All fleas have the same four life cycle stages: embryo, larva, pupa, and adult. This whole life cycle from egg to adult takes from two to three weeks, although this depends on the temperature. It may take longer in cool conditions.

Wikipedia – Cat Flea