Cat flea eggs are 0.5 x 0.3 millimeters, translucent, white and oval-shaped. A single female flea produces 20 to 30 eggs per day (one egg per hour). She will lay around 175 viable eggs during her normal lifespan, which lasts seven days a host.
Cat fleas lay their eggs directly in the animal host’s fur. Most of the eggs fall off the host and into the environment within 2 hours, getting concentrated around pet resting areas. The eggs hatch into larvae within two to three days.
Cat flea eggs are 0.5 mm long and 0.3 mm wide. While minuscule in size, the eggs can still be seen by the unaided human eye.
Freshly laid eggs glisten and are a translucent, off-white color. As they develop, the eggs become slightly darker and more opaque, looking almost pearl-like. Larvae can be seen within late stage eggs.
Img 1 Cat flea eggs on the tip of a human finger.
Cat flea eggs are a rounded oval shape. The chorion (outer shell) is smooth and has very few surface structures. Newly laid eggs are wet and sticky, but they dry rapidly and become non-adherent.
When Egg Production Begins
In order to lay viable eggs, cat fleas must feed and subsequently mate. Unfed females cannot lay eggs due to their underdeveloped ovaries. Consuming a blood meal triggers sexual maturity. Similarly, male fleas must first feed to be able to successfully mate.
Egg production occurs in virgin females, but the eggs won’t be viable. Upon mating males, the eggs become viable and output quadruples. Fertility is highest when females mate with multiple male partners.
Adult fleas immediately seek a host once they emerge from cocoons. They will begin feeding within minutes of acquiring a host. Mating occurs 8 to 24 hours after host acquisition. Females begin laying eggs one to two days after the first blood meal.
Reproductive Biology of Fleas
Female cat fleas have two ovaries, each composed of six ovarioles. These 12 ovarioles produce around 20 eggs a day. Each ovariole can produce at least 50 oocytes (immature egg cells) during a female’s life. In theory, a single flea may lay as many as 400 to 900 eggs during her lifespan, and actual studies show this is a conservative estimate.
During active reproduction, a female flea will typically have six eggs contained in her abdomen at any given time. In rare instances, a female’s abdomen may carry up to 13 mature eggs.
Rate of Egg Production
Cat fleas are highly reproductive. A healthy female will produce an average of 20 to 30 eggs per day, depositing roughly one egg per hour. Amazingly, a female flea produces her body weight in eggs everyday.
Fig 1 Number of eggs produced per cat flea (y-axis) at every hour across a day (x-axis). The scotophase (dark cycle) occurred from 1800 to 0600 hours.
Two to three days after the initial blood meal, oviposition begins at a rate of five to ten eggs a day. Peak egg production occurs four to nine days after the first blood meal. An average of 25 to 30 eggs are laid per day during peak production. At a maximum, a single female was observed producing 46.3 eggs a day. A relatively high rate of production is maintained for two to four weeks before gently tapering off.
Egg production will continue for as long as the female flea survives. However, the rate of deposition progressively decreases with age. A 113 day old female is capable of producing four to five eggs a day.
Flea Lifespan & Fecundity
Adult cat fleas have a lifespan of about seven days when living on a host. A majority of fleas die due to host grooming. When host grooming is restricted, fleas are capable of surviving for over 100 days. The maximum lifespan was observed at 185 days.
In the past, average fecundity was believed to be near 800 eggs. More recent studies conclude that a female cat flea will lay less than 200 viable eggs during her normal lifespan. This is a reasonable number, considering the average life of a female is seven days and she produces 25 eggs a day (totaling 175 eggs). However, over 2000 eggs can be a produced by a single female if she is able to survive for over 100 days. Reproductive capacity is nears depletion by the third month of continuous egg production.
Where Fleas Lay Eggs
Adult cat fleas live on their host, rarely leaving of their own volition. Generally, adult fleas will only abandon their host when it is dead or dying. They won’t leave even when on-host populations reach very high levels.
Img 2 A cat flea laying an egg in a dog’s haircoat.
Female fleas must feed regularly in order to keep their metabolism in balance for egg production. Thus, female cat fleas feed, mate and lay their eggs directly on the host. The eggs gets deposited into the fur (pelage) of the host animal.
The Eggs Fall Off the Host
Freshly laid flea eggs are wet and sticky, which prevents them from falling off the host immediately. However, the eggs dry quickly and become non-adherent thanks to their ovoid shape and smooth chorion. The eggs fall so easily from hosts that grooming habits are of little significance for dislodgement. A majority of the eggs will drop from the host within two hours of deposition.
The dislodged flea eggs fall out of the infested animal’s pelage and into the surrounding environment. They are continually being dropped from the host, and can get distributed anywhere the animal has access to. Movement and behavior patterns of pets will determine where the flea eggs get dispersed. Most of the eggs fall off inside of homes, and clumped around areas where pets habitually sleep, rest or feed.
To successfully hatch and continue developing, flea eggs must fall onto substrates with a warm, humid microclimate. A relative humidity between 75% and 92% is optimal. Desiccation often occurs below 50% RH. Ambient temperature must be between 55.4°F (13°C) and 100.4°F (38°C) for egg survival.
Fig 2 Environmental conditions required for flea eggs to survive, and days it takes for the eggs to hatch into larvae.
To successfully develop, these habitats also must have an accumulation of adult feces for larvae to consume once they hatch. Adult fecal blood becomes dislodged when hosts groom themselves. Thus, locations where both eggs and “flea dirt” reside tend to be in host resting locations where grooming takes place.
Where the Eggs Incubate
In homes, most immature fleas develop within carpet fibers. Modern carpets create the near ideal microhabitat for eggs and larvae to develop in. The carpet canopy provides protection from desiccating air flow, sunlight, vacuum removal and insecticide penetration. In addition, it accumulates larval food.
Flea eggs end up concentrated in carpeted rooms where pets spend most of their time. Bedrooms and living rooms often have the highest number of immature fleas. Within these rooms, the eggs and larvae will be found clumped around areas where dogs or cats sleep, such as at the side of a bed.
Outdoor locations for viable egg development are more rare than indoor locations. The eggs will not survive in open, sun-exposed areas. They must be protected from fluctuations in weather conditions. Common locations to find flea eggs outside include in dog houses, pet shelters, under porches and beneath dense ground cover.
How Long Flea Eggs Live For
The incubation period for cat fleas eggs is brief. In a home environment, they will hatch into larvae within two to three days. The eggs can develop in as little as 36 hours in a warm, humid environment. In poor conditions, it may take eight to twelve days for fleas eggs to hatch.
Fig 3 Days it takes (y-axis) for 50% of flea eggs to hatch at different ambient temperatures (x-axis) while relative humidity is held constant at 75%.
Ambient temperature is the primary factor regulating flea population growth. When relative humidity is held constant at 75%, the optimal temperature occurs at 89.6°F (32°C), with 50% of the eggs hatching within 1.5 days. Time to hatch increases as temperatures decrease (Fig 3).
Fig 4: Percent of eggs that survive (y-axis) at three different ambient temperatures across 10 days (x-axis).