|Female cat flea|
The cat flea (scientific name Ctenocephalides felis) is an extremely common parasitic insect whose principal host is the domestic cat, although a high proportion of the fleas found on dogs also belong to this species (this despite the widespread existence of a separate and well-established "dog" flea, Ctenocephalides canis).
The cat flea belongs to the insect order Siphonaptera (Ancient Greek siphono- "tube" or "siphon" + a "not" + ptera "wing", the tube-drinking wingless insects) which in its adult stage is an obligatory hematophage. Adults of both sexes range from 1–2 mm long and are usually a reddish-brown colour, although the abdomens of gravid females often swell with eggs causing them to appear banded in cream and dark brown. Like all fleas, the cat flea is compressed laterally allowing it to slip between the sometimes dense hairs of its host just above the top layer of the skin, resulting in an extremely thin insect that may be difficult to observe even if the host's coat is pure white.
The cat flea's primary host is the domestic cat for which it has a distinct feeding preference, but it is also the primary flea infesting dogs in most of the world. The cat flea can also maintain its life cycle on other carnivores and on omnivores, but these are only chosen when more acceptable hosts become unavailable. Adult cat fleas do not willingly leave their hosts, and inter-animal transfer of adult fleas is rare except in animals that share sleeping quarters. A flea which becomes separated from its host will often die within hours from starvation.
Although humans are susceptible to bites from this insect, such bites tend to be rare and are all but unheard of if a more suitable host (i.e., a cat) is anywhere within the vicinity, especially as the adult insects only become separated from their hosts accidentally. While some research has shown that a female cat flea, if allowed to feed undisturbed for 12 consecutive hours on a human, may be capable of producing at least some viable eggs after mating, a long-term population of cat fleas in a human-only environment has never been shown to be sustainable.
Flea populations are distributed with about 50% eggs, 35% larvae, 10% pupae, and 5% adults.
An adult gravid female flea that has consumed a full blood meal will begin to produce between 20 and 30 microscopic (0.5 mm) non-adhesive white ovoid eggs per day, laying them individually and continually at a rate of about one per hour until she dies (under ideal conditions it might be possible for her to produce between 2,000 and 8,000 eggs in her lifetime, though most only manage to produce around 100 before being consumed by their host during grooming activity). The eggs are dispersed freely into the environment. Within two to seven weeks a certain proportion will then hatch into larvae.
The larva of the cat flea has a grub-like appearance and is ~2 mm in length. The larvae are negatively phototaxic/ phototropic, avoiding light and hiding in the substrate around them. The larvae require adequate ambient moisture and warmth, and will die at temperatures near freezing. While in this developmental stage the larvae will feed on a variety of organic substances, but the most important dietary item for them is the crumbs dried blood that continually fall like snow out of the haircoat of the host after it has been excreted by the adult fleas as fecal material. Thus, the adult flea population continually feeds the larval population in the animal's environment.
Flea larvae metamorphose through four stages before spinning a cocoon and entering the pupal stage. The cocoon is adhesive, and quickly acquires a coat of camouflage from surrounding dirt and dust. Pupation depends heavily on temperature and moisture, and take a week or more to complete, though a fully pupated adult can remain inside of its cocoon in a state of semi-dormancy (called the "pupal window") awaiting signs of the presence of a host. 
Newly emerged fleas use variations in light and shadow along with increases in warmth and CO2 to detect the presence of a potential host, and will jump to a new host within seconds of emerging from the cocoon. The new flea begins feeding on host blood within minutes.
Effects on the hosts
A few fleas on adult dogs or cats cause little harm unless the host becomes allergic to substances in saliva. The disease that results is called flea allergy dermatitis. Small animals with large infestations can lose enough bodily fluid to fleas feeding that dehydration may result. Cat fleas also may be responsible for disease transmission through humans, and have been suspected as transmission agents of plague.
Cat fleas can transmit other parasites and infections to dogs and cats and also to humans. The most prominent of these are Bartonella, murine typhus, and apedermatitis. The tapeworm Dipylidium caninum can be transmitted when an immature flea is swallowed by pets or humans. In addition, cat fleas have been found to carry Borrelia burgdorferi, the etiologic agent of Lyme disease, but their ability to transmit the disease is unclear.
Since more than three-quarters of a flea's life is spent somewhere other than on the host animal, it is not adequate to treat only the host; it is important also to treat the host's environment. Thorough vacuuming, washing linens in hot water, and treating all hosts in the immediate environment (the entire household, for example) are essential and if possible on a regular basis.
- Pulicosis (Flea bites)
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|Wikimedia Commons has media related to Ctenocephalides felis.|
- Integrated Flea Control from University of Nebraska-Lincoln Extension in Lancaster County
- cat flea on the UF / IFAS Featured Creatures Web site
- About Ctenocephalides felis (cat flea): taxonomy, life cycle, transmitted diseases, eradication at MetaPathogen
- Dog flea treatments
- Finding and Eliminating Fleas on Your Cat from the BBC
- Safe Use of Flea and Tick Products in Pets