Flea Eggs in Cats and Dogs:
Why They Matter

Flea eggs are hard to spot.

If we didn't tell you about them, you probably wouldn't be aware that they infest your home or garden.

They are tiny and can be mistaken for dirt, sand, or dandruff if you don't scrutinize them.

But they must be considered in your flea treatment choices. 

And that's because there are so many of them: eggs make up more than 50% of the life forms of fleas. And they continuously feed the reinfestation of your home.

Now let's look at what they look like, their influence on the infestation dynamics, and how to eliminate them.

Eggs in the flea life cycle

90% of fleas on pets are cat fleas or Ctenocephalides felis. The other species, the dog flea, or Ctenocephalides canis, is much rarer. Both species infect dogs, cats, and many wild animals, such as opossums, raccoons, or foxes. They may occasionally bite humans on the feet, ankles, and lower legs.

Female fleas are very prolific. They can reproduce amazingly rapidly and lay many eggs: up to 1,700 in their lifetime^[1].

The adult cat flea begins feeding within minutes of landing on its host, and the female starts laying eggs 24 hours later^[2]. They can lay up to 50 eggs per day and 24 on average^[3].

Upon hatching, the eggs are moist and stick to the animal's fur. By drying quickly, they detach from the hair and fall to the ground.

This is why they can be found in all the places where animals spend time: where they pass by, sleep, rest, or feed. Of course, the eggs are inert and cannot burrow deep into the ground as larvae tend to do.

Flea eggs accumulate in your home into an ever-growing reservoir that fuels the persistent infestation of your pets.

Think about it for a moment: every flea you detect on your pet can generate about 1,000 new fleas.

That's scary, isn't it?

Fortunately, many flea eggs die:

• they don't hatch
• they are ingested by predators: flea larvae, spiders, and other insects
• they are disposed of when you clean up

When they hatch, flea eggs give birth to first-stage larvae.

What do flea eggs look like

Flea eggs can be seen with the naked eye. But they are tiny.

Flea Eggs, picked up from John's Sweater by Denni Schnapp

They are oval, smooth, about 0.5 mm in size, and fall out of the dog’s coat in the immediate environment.

What color are flea eggs

Just after the hatching, flea eggs are pearly white, almost transparent. As the maturation progresses, the color darkens toward brown.

Where are flea eggs found

Flea eggs are found in areas where your animal usually sleeps, rests, or feeds. As they can’t move, they can’t hide deep in carpets or crawl under pieces of furniture as larvae do. They are especially vulnerable to vacuum cleaning.

When do fleas lay their eggs?

Fleas have adapted to their host’s way of life: they lay more eggs at times of day when animals usually rest or sleep.

It creates there a micro eco-system where eggs, flea dirt (same as flea feces), and larvae are concentrated. This is beneficial to the development of flea larvae whose primary food sources are precisely eggs and flea dirt.

Correspondence of flea egg laying times with cats sleeping/resting times^[3]

How long does it take for flea eggs to hatch?

In optimal conditions, i.e. 95°F (35°C) and more than 70% of relative humidity (RH), it only takes 1 day for a flea egg to hatch. The more the actual conditions are far from these figures, the longer it will take for a flea egg to hatch, up to 10 days. A relative humidity lower than 50% or a temperature lower than 32°F (0°C) is lethal.

Identifying flea eggs

Dog or cat dandruff or flea eggs?

With careful examination and good eyes, you should be able to tell the difference between dandruff and flea eggs.

When they reside on the pet's coat, flea eggs are pearly white, with a regular 3-D oval shape, and are all of equal size (about 0.5 mm). They do not stay more than a few hours on the animal's coat. When they dry, they roll off quickly and fall to the ground.

Dandruff is made up of whitish flakes of skin. They are flat and differ substantially in size. Peeling is continuous, and the distribution of dandruff on the coat is uniform.

Dandruff is the manifestation of an inflammatory skin condition called desquamation which consists of excessive exfoliation of the epidermis.

Dandruff is common in dogs but unusual in cats partly because they groom themselves thoroughly. You'll notice it more often in older cats who groom less.

Scaling is caused by irritation, allergy, or some underlying metabolic diseases such as hypothyroidism or hyperadrenocorticism. The presence of dandruff in cats suggests infection by the fungus Malassezia.

Flea eggs on bed sheets

This is a common question from some owners of flea-infested pets.

We will see that there is not much to worry about.

There are 3 situations to consider:

1. Is your dog or cat allowed to walk or sit on your bed? If not, there is no chance you will see flea eggs on your sheets, as they will necessarily fall off your pet's coat.

2. Can you see flea feces? Flea feces fall in the exact same places as the eggs. These droppings look like dark dust. To check if the dust you have collected is from fleas, put it on a damp piece of paper. If you notice a red discharge (i.e., undigested blood from flea meals), chances are you also have flea eggs in your bed.

3. Do you have itchy red spots on your ankles and legs? This may also indicate that your home is infested with fleas.

How to kill flea eggs

Killing flea eggs means making them non-viable, which means either:

- They won't hatch

- or the resulting larva will not develop into a viable adult.

It will help break the life cycle of fleas and prevent the reinfestation of your pets.

Killing flea eggs in your home

The first step is to identify where the eggs are most likely to be found: the areas where your pet lives or frequently visits.

It is recommended to clean or vacuum these areas (preferably with a vacuum cleaner equipped with a beater). Since flea eggs do not move, most are accessible and can be easily removed.

The other way is to spray these areas with insect growth regulators (IGR). This is a helpful supplement for areas that cannot be washed easily (carpets, upholstery, cushions, dog beds, etc.).

These sprays contain either methoprene or pyriproxyfen. They have a persistence of about 2 months and are very effective if you apply them correctly, i.e., if you target the right areas.

Refrain from using foggers because they won't reach every corner of your room.

These treatments are not a substitute for proper flea treatment of your pet.

Killing flea eggs on the pet ^{[4], [5], [6], [7]}

This treatment can only be done with approved flea control products. They guarantee effectiveness and safety for both the animal and the owner(s).

Experts and licensees recommend 3 different strategies.

1. Kill the adult fleas on the animal before they have time to lay eggs.

Simple and effective method on condition that the anti-flea product is:

• fast enough to kill all fleas within 24 hours after they land on the animal, thus not giving the fleas the time to mate and start laying eggs
• 100% effective for the entire control period claimed by the marketing authorization

This strategy has been made possible by the discovery of new, very effective products, particularly those containing molecules of the isoxazolines chemical family (Bravecto®, Credelio®, Nexgard®, and Simparica®).

Another great advantage is that your pet (and your home) is protected even if the infestation occurs outside.

The main weakness of this method is you! You need to comply with the treatment schedule.

If you forget to apply the second treatment on time, the flea infestation cycle will start again.

2. Addition of an IGR to older but still effective adulticidal molecules

IGR stands for Insect Growth Regulator. These molecules prevent the eggs from hatching and larvae from molting. They break the life cycle of fleas.

2 molecules are currently available:

• methoprene is commonly combined with fipronil (Frontline® Plus or Combo and generics), permethrin (Duowin®), or natural pyrethrins (Adams Plus®)
• pyriproxyfen is frequently associated with fipronil (Effipro Duo ®), dinotefuran (Vectra 3D®), permethrin (Ectoline Duo®), and imidacloprid (Advantage® and Advantix® and generics),

These products exist in the form of drops (the most practical), flea bombs, or flea shampoo.

Note that permethrin should not be used in cats, as they can become intoxicated by licking their fur impregnated with the molecule.

The IGRs applied to the animal are effective in two ways:

• On the animal, they are taken up by adult female fleas whose eggs become non-viable.
• On the ground, flea eggs and larvae may come in contact with pet hair or flea feces treated with IGRs. They will be prevented from hatching or molting.

Because they act on different stages of flea infestation, IGRs reinforce the effectiveness of adulticidal molecules, and they help break flea lifecycle in the long run.

The other great advantage is that there are many inexpensive generics available.

Because they act on different stages of flea infestation, IGRs are effective in the long term.

In addition, you can find many inexpensive generics that will make the treatment more affordable.

3. Program® and Capstar® combined in a flea treatment system

Capstar® and Program® are both oral tablets. They pass into the animal's bloodstream and reach the fleas when they bite.

Lufenuron, the active ingredient in Program®, blocks the formation of chitin. It prevents the development of flea larvae from the eggs but does not kill adult fleas. It must be administered every month.

Nitenpyram, the active ingredient in Capstar®, kills sucking fleas very quickly but has a short persistence, about two days. According to the label, it should be administered once or twice weekly.

This is a constraint: no one wants to give a flea medication every few days.

But these two molecules are worth considering, and you can freely combine them at a lower cost.

If you are patient and can tolerate your pet having a few fleas for a few weeks, you can start with a Capstar® tablet and continue with the Program® for a few months to get rid of the infestation and sanitize your home.

If you are less patient, you can replace Capstar® with a more modern product that will control adult fleas for at least a month.

And there's a bonus if you have a cat. You can ask your veterinarian to inject the long-lasting form of Program®, and she'll be protected for 6 months!

Conclusion

Flea eggs are hard to spot, and you may not be aware of their presence if you're new to flea control.

But they deserve your attention. They are the most numerous of all life forms of fleas and constitute an enormous reservoir for future infestations.

Targeting them is an essential part of any conscientious flea control strategy.

Gilles Ventejol

Gilles Ventejol is a professional in Animal Health. He holds a master's degree in life sciences. He has worked for more than 20 years in veterinary pharmaceutical companies, where he contributed to the development and promotion of many veterinary drugs. In this context, he has organized numerous conferences for the veterinary profession. His areas of expertise are parasitology, cardiology, nephrology, vaccines, and reproduction.