Img 1 A female cat flea laying an egg in a dog’s haircoat.
Female fleas lay eggs on their host. On cats, most fleas live around the neck. On dogs, they’re more often found around the hips. Flea eggs aren’t sticky, so they’ll soon fall from the animal’s fur. The eggs accumulate in areas where pets rest, namely carpeting.
Where Eggs are Laid
Fleas are Permanent Ectoparasites
Adult cat fleas are permanent residents of their hosts. They’ll rarely leave of their own choosing. When grooming is restricted, 85% of female and 58% of male fleas will stay on the animal for over 50 days. Few fleas transfer between hosts, even when cats live together. Fleas usually only abandon a host if it’s dead.
Eggs are Laid on the Host
Where Fleas Live on Dogs & Cats
On cats, most fleas live on the dorsal area, namely the neck and collar. On dogs, they’re more likely to live around the hindquarters. Fleas prefer living in regions which are infrequently groomed by the host. It can be assumed that eggs get laid near these areas as well.
The Eggs Fall Off the Host
Flea Eggs aren’t Sticky
Cat flea eggs have a rounded oval shape. The shell’s surface is smooth. Freshly laid eggs are wet and sticky, so they don’t immediately fall from the host. However, they dry rapidly. And, once dry, the eggs become non-adherent. They’ll then readily fall from the animal, even without grooming.
How Quickly the Eggs Fall
In one study, 60% of flea eggs fell from a cat within two hours of being laid. 65% had dropped off by the fourth hour. Close to 70% were dislodged by the eighth hour. At this point, only 2.3% of the eggs remained on the host. The other 27.7% were believed to be consumed by the cat during grooming.
How quickly the eggs fall depends upon the host’s grooming and movement habits, as well as its hair length. A small percentage of eggs may become lodged in a pet’s fur, especially if the hair coat is dense and dirty.
Where the Eggs Fall
Dislodged eggs drop into the environment, both indoors and outdoors. They continually fall, getting distributed anywhere an infested animal can access. A pet’s movement and behavior patterns dictate where the eggs get dispersed. Most get deposited inside of homes, and clumped in areas where pets habitually sleep, rest, and feed.
Flea eggs accumulate in resting sites because oviposition and egg shedding peak at night, when domestic dogs and cats sleep. In addition, cats spend most of their time sleeping, resting, and grooming. They’re only active for 13% of the day. Cats also commonly share preferred resting sites with other cats.
Though there’s a clumped distribution, eggs still get widely dispersed around a host’s movement range. Less than 50% of larvae live in areas where a cat spends 90% of its time, and larvae rarely travel far from where they hatch.
Only the eggs which fall onto substrates with specific habitat requirements will successfully develop. Viable incubation zones aren’t widespread around homes.
Humidity & Temperature
Flea eggs are susceptible to desiccation. To successfully hatch and continue developing, they must fall onto substrates with a warm, humid microclimate. A relative humidity (RH) between 50-92% is optimal for flea eggs. Desiccation occurs below 50% RH. Ambient temperature must be between 50.4°F and 100.4°F (10°C and 38°C) for eggs to survive.
Fig 1 Environmental conditions required for flea eggs to survive, and days until they hatch.
Adult Fecal Blood
Without food, flea larvae will starve to death within three days of hatching. Their primary food source is the feces (flea dirt) of adult fleas. For fleas to successfully develop, eggs must fall into habitats that contain plenty of fecal blood. Flea dirt doesn’t fall from hosts as easy as eggs. It’s typically only dislodged during grooming. So, areas containing both eggs and feces tend to be where hosts groom themselves.
Where Flea Eggs Incubate
In homes, most immature fleas live within carpet fibers. Carpeting creates a near ideal microhabitat for eggs and larvae. The canopy protects them from sunlight, air flow, vacuuming, and insecticides. It also traps food for larvae.
Flea eggs end up concentrated in rooms where pets spend the most time, namely bedrooms and living rooms. Within these rooms, eggs amass in areas where dogs or cats sleep, such as at the side of a bed or sofa.
Common Incubation Zones
The most common places to find flea eggs indoors include: Carpeting, rugs, floorboard cracks, pet bedding, cushions and upholstery, beneath beds and furniture, and dirt floor basements.
Uncommon Incubation Zones
Fleas rarely develop in carpeting that gets a lot of sunlight, or in well-traveled areas like hallways. Few eggs will successfully hatch on wooden floors, and even fewer on tile or linoleum. However, they may develop within the cracks of these floor types.
Outdoor Survival is Rare
Viable habitats are more rare outdoors than indoors. Flea eggs won’t survive in open, sun-exposed areas. They need to be sheltered from fluctuations in weather conditions. Habitats must be shaded and shielded from the wind, with relative humidity exceeding 45% at all times. Grass, for example, isn’t a suitable habitat. In addition, eggs dropped by roaming hosts usually won’t survive, because they are unlikely to fall near flea dirt.
Common Incubation Zones
The most common places to find flea eggs outdoors include: Dog houses, pet shelters, flower beds, gardens, crawl spaces, dense ground cover, vegetation around structures, feral animal nests, and areas where pets go to escape the sun’s heat. For example, animals often seek shade under homes or decks.