Flea Pupae
Appearance, Biology and Treatment
Carpet photo by Tincho Franco on Unsplash
Cat fleas are holometabolous insects. They belong to the category of insects that must undergo a complete metamorphosis to pass from the larval stage to the adult flea stage.
The pupa represents this transition stage.
The pupa is the stage of resistance among the 4 stages of the life cycle of fleas. That is, it is the stage where the flea is most resistant to external conditions.
It is also the stage during which the flea can live the longest, waiting for the arrival of its new host.
The existence of this crucial stage helps explain why it is often so difficult to get rid of fleas in the home.
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Useful definitions
Pupa:
The pupa is the life stage between the larval and adult (imago) stages of the flea and where it undergoes a complete metamorphosis. The pupa is non-motile and usually enclosed in a cocoon.
Cocoon:
An envelope made of the silk secreted by the flea larva and wrapped around its body just before it begins metamorphosis.
Nymph:
You may sometimes come across this name, but it does not apply to fleas. It refers only to insects (ametabola or hemimetabola) that do not undergo a complete metamorphosis. It is the last stage before the insect becomes an adult. It resembles the adult but smaller and without wings (grasshoppers, bugs...).
What is insect metamorphosis?
Metamorphosis is a strong term.
In the case of insects, it is an awe-inspiring process, which still leaves many scientists amazed.
The complete metamorphosis of an insect consists of an abrupt and radical change in its morphology, behavior, and diet. It occurs between the larval and adult stages when the insect is a pupa.
Hormonal regulation
In insects, the passage from an immature form to another is regulated by 2 hormones:
- The Juvenile Hormone is continuously present during all larval stages and maintains the insect in an immature state
- The short-lived ecdysone triggers the molt toward the next stage
When the Juvenile Hormone eventually disappears, the following ecdysone surge provokes the molt toward the pupal stage.
Tissue destruction and regeneration
Metamorphosis is closely related to embryogenesis.
Embryogenesis is the process that builds the structure of a living animal and all its organs from one egg, that is, from a single cell that divides and specializes.
In the case of holometabolous insects, and therefore of cat fleas, the embryogenic process is not completed in the egg. It is interrupted to give birth to a larva.
When it becomes a pupa, the insect resumes its path toward the adult stage. The larval tissues are destroyed, and adult organs appear: legs, eyes, wings, mouth parts, etc.
The advantages that holometabolous insects derive from this developmental strategy are still a matter of debate. At least, it allows immature forms to quickly and easily colonize nutrient-rich habitat types (soils, water) and gives these insects time to develop more sophisticated strategies for reproduction.
Metamorphosis is considered by specialists to be a higher rung on the evolutionary ladder.
If you want to know more about the subject, I suggest you read the following article:
The Evolution of Insect Metamorphosis by James W. Truman
The pupa in the life cycle of cat fleas
At the end of its third larval stage, the cat flea (Ctenocephalides felis) weaves a silky cocoon around itself, folds in 2 (in the shape of a V), and begins its transformation.
Flea third stage larva surrounded by a silky cocoon
The cocoon protects the pupa while it is immobile and defenseless. It retains some moisture, so the pupa is less susceptible to desiccation than the larvae. In addition, because of the sticky nature of the cocoon, various types of debris adhere to it and help the pupa camouflage and protect itself from predators: ants, spiders, flea larvae...
Flea pupa undergoing metamorphosis
The pupae live in the same places as the larvae. They never move.
In optimal conditions: 24-27°C and 78-80% humidity, the cat flea metamorphosis lasts from 5 to 9 days[1],[2]. It lasts longer if these conditions are less favorable.
Extreme temperatures below 3°C or above 35°C cause pupal death.
Once metamorphosis is complete, the adult flea may remain quiescent in its cocoon for an extended period of time, up to one year, if it does not detect signs of a potential host nearby. The pupa is then called a pre-emerged adult[3].
Flea pre-emerged adult still protected by its cocoon
This last point is essential: the pupa is the resistant stage of the flea life cycle. Your pet may be infested with fleas from places not visited by an infested animal (your pet or another cat or dog) for a very long time.
Stimuli that awaken pre-emerged adults are vibrations, a sudden increase in temperature or humidity, an increase in CO2 concentration, or a draft[4].
If the emerged young adult finds a suitable host, i.e. a dog or a cat, it will stay, live, feed, and reproduce there. If it happens to find only a human, it will occasionally feed on the lower part of legs without setting on the hair. It will move to a cat or dog soon as it can.
Where can I find flea pupae
Once a last stage larva has begun to spin a cocoon, it doesn't move until it becomes a full adult. This means that pupae can be found in the same places as larvae, eggs, or flea feces: where infested pets usually rest or feed.
Larvae prefer dark places and try to hide in the depths of carpets, in the fabric of furniture, or between floorboards.
Flea pupae in flea control
Should you target flea pupae?
Eliminating flea pupae is part of the flea control strategy in the environment.
It involves the same measures as for treating the other immature forms of the cat flea: larvae and eggs.
This can be done mechanically (cleaning, vacuuming) or chemically (commercially available sprays) in infested areas.
But you must be aware that you cannot eliminate 100% of flea pupae because they are hidden deep in your carpets, in the cushions of your sofas or armchairs, or in the dark and sheltered areas of your garden[5].
Should you consider flea pupae in your home or garden?
Even if you cannot hope to destroy all the flea pupae in your home or garden quickly, it is absolutely necessary to be aware of their existence.
Why?
Because it is the flea's life stage that allows the flea infestation to continue over time.
The pupa is the most resistant stage of the flea life cycle:
- It is the most tolerant form to extreme temperature and humidity conditions
- It is not always sensitive to insect growth regulators (see below)
- It is protected by its cocoon, and often surrounded by various debris that reinforces protection from predators
- They have the longest potential life span
This allows fleas to reappear long after the last adult flea has been killed by an insecticide treatment.
In practice, even if you eliminate all fleas from your pet(s), you should be aware that your home and yard are still infested, and you will need to watch for fleas to reappear.
What kills flea pupae
Although flea pupae are more challenging to eliminate than larvae, the same treatment and method are recommended: find the areas where these immature forms are found and treat those areas thoroughly.
In your home
At home, the real challenge is treating pupae that live in carpets or upholstery, because they are hiding there and are difficult to reach by mechanical or chemical means.
Mechanical treatments
They should not be neglected because they are a real help in controlling the flea population. They eliminate a large part of the eggs and larvae, as well as some pupae.
They consist of washing any washable item with which your pet is regularly in contact every week.
You should also wash/clean tiled and wooden floors.
Carpets should be vacuumed every 2-3 days, especially before applying a chemical treatment. This will straighten the carpet pile to get the product deeper into the carpet, where many of the pupae reside.
Chemical treatments
You can find on the market different types of sprays to treat your home. They are usually called "Home Spray", "Carpet Spray", "Upholstery Spray" or "Pet Bedding Spray".
These products typically contain a combination of a neurotoxic insecticide and an insect growth regulator (IGR)
- The IGR can be methoprene, pyriproxyfen, or fenoxycarb. They mimic the action of the juvenile hormone and prevent larvae from developing into pupae or newly formed pupae from developing into adults[6].
- The neurotoxic insecticide is a natural or synthetic pyrethrin (permethrin, deltamethrin, etofenprox, tetramethrin, or bifenthrin) or imidacloprid. Pyrethrins are known for their repellent effect and very low toxicity on mammals. Under laboratory conditions, they are effective on pupae of all developmental levels.
The problem is that these molecules must be able to come in contact with the parasite, larva or pupa. But carpets offer very good protection for immature fleas. We should not expect more than 50% effectiveness. But it is a welcome contribution to flea control in case of heavy infestation.
We do not recommend using herbal or "natural" products, as there is very little documentation on their effectiveness.
In your yard
Immature fleas look for dark places and avoid sunlight.
Also, be aware that flea eggs can be laid by fleas living on wild or feral animals that occasionally visit your yard. You should try to avoid their presence by fencing your yard or using repellents.
You should keep your lawn cut short to keep the flea larvae exposed to the sun.
There are also specialized products for treating your yard. They contain permethrin or imidacloprid. Apply them in dark places that never see the sun (under a bridge, in the shadow of a hedge...)
Flea Pupae Frequently Asked Questions
Do flea pupae move?
Flea pupae can't move. They remain quiescent in a cocoon until they find a new host. They then emerge from the cocoon, but they have now become adults.
Do flea pupae bite?
Flea pupae don't bite. If they've just started their metamorphosis, their mouthparts are still adapted for chewing, not biting. Once they've completed their metamorphosis, they remain quiescent as pre-emerged adults. If they detect a host, they leave their cocoon, jump on the cat or dog and then bite. But they are no longer pupae, they are adults.
How long do flea pupae live?
From 5 days to one year. Under favorable conditions, it takes 5 to 9 days or the larva to metamorphose into an adult. Protected by its cocoon, the pupa can remain dormant for an extended period of time up to one year, until favorable conditions are met.
Conclusion
The pupa is the more resistant stage of the flea life cycle:
- It is well protected from predators due to its cocoon being surrounded by various debris stuck to it
- It is more tolerant to extreme temperatures and humidity than the other stages
- It in't easy to reach because it is often hidden in the carpets and upholstery of your home or deep grass or hedges of your yard
- Most importantly, it can stay quiescent for months waiting for favorable conditions, making it a long-lasting reservoir for a new infestation
You can't hope to achieve proper flea control by targeting flea pupae alone. But you must be aware they are present in your home or yard as an inevitable consequence of a previous flea infestation on your pet.
Main References
1. W. H. Miller, C. E. Griffin, K. L. Campbell.Muller and Kirk's Small Animal Dermatology, 7th Edition. p323
2. M. J. DAY.Arthropod-borne Infectious Diseases of the Dog and Cat, Second Edition. p19
3. C. Noli, S. Colombo.Feline Dermatology. 2020. p443
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.
