This is a tricky question and depends on what stage in their life cycle the flea is in. The short answer is: no, fleas are not attracted to light, but rather the shadows of potential prey against a light background; and yes, they are attracted to body heat. Fleas use light and heat stimuli, along with movement and exhaled carbon dioxide, to find a host.
Flea Life Cycle
Fleas need different things during different stages of their life cycles, and while you’re most likely more worried about adult fleas than flea larvae, knowing where they thrive at different stages can help to combat them in your home.
The full life cycle of a flea can be completed in about 20 to 35 days under ideal conditions, and there are four stages: egg, larva, pupa, and adult. Ideal conditions for fleas are about 85 degrees F and 85% relative humidity.
Eggs. Flea eggs are tiny — only about 1/50 of an inch long. The female flea will lay eggs after her first blood feeding and those eggs can fall off of the host onto the ground, carpet or bedding of your pet.
Larva. Eggs hatch into larva in 2 to 14 days. Larva start out small, 1/16 of an inch and grow by molting, or shedding their skin, to about 1/4 inch. This process can take anywhere from 8 to 24 days, depending on conditions.
Larva live where they hatch — deep inside carpet fibers, pet bedding, or vegetation, where it’s dark and moist. They eat organic debris and flea feces, which contains partially digested blood.
Pupa. Once the larva is fully grown, it will spin a sticky cocoon where it will remain inactive. This stage can last from 5 to 7 days, but can last up to a year in unfavorable conditions.
Adult. Adult fleas will emerge from the cocoon when stimulated by a potential host passing nearby. They have powerful hind legs that help them jump up to 8 inches vertically and 16 inches horizontally in pursuit of a host.
Adult females will begin laying eggs, 2 to 14 at a time and up to 800 in their lifetime, immediately after their first feeding, beginning the cycle over again.
Are Fleas Attracted to Light?
In their larva stage, fleas shy away from light and prefer to spend their time close to the skin of their host, hidden in fur, or deep in carpet or grass. It isn’t until their adult stage, about a month after the eggs were laid, that fleas come to the surface in pursuit of a host.
Adult fleas are sensitive to yellow-green light and are attracted to dark moving objects against that light background. It’s also possible that intermittent light can mimic the shadow of a host passing, and fool fleas into pursuing it. In a study on commercially available flea traps, researchers discovered that traps that used irregular lighting captured more fleas when compared to traps that used continuous lighting.
So while fleas do use light in their search of food, they’re not really attracted to the light — they’re attracted to shadows cast by potential hosts. But they don’t rely on shadows alone: Fleas are also attracted to heat and carbon dioxide.
Are Fleas Attracted to Heat?
Fleas are attracted to heat in the sense that the body heat of a passing host can trigger adults to emerge from their cocoons and pursue the source. Fleas in the pupal stage will remain inactive until stimulated, by heat as well as other factors, to emerge.
Fleas can remain inside their cocoons in the pupal stage for up to a year waiting for the right stimuli. Once they emerge, adult fleas will jump towards their potential host. But heat alone won’t stimulate an adult flea to emerge from their cocoon. They also require movement, changes in light intensity, and exhaled carbon dioxide.
Where do Fleas Hide?
Fleas need warm, humid environments and you’re most likely to find them in the places their hosts spend the most time. If your pet has fleas, that means their bedding or even your bedding are likely hiding places for flea eggs, larvae, and pupae.
You also can find them in dark, moist places, like your garden soil, and in carpet fibers, beneath furniture and under beds. This is why it’s so important to vacuum and wash bedding regularly to disrupt their life cycles and prevent future fleas.
How to Prevent Fleas Naturally
Keeping carpets and bedding clean is one of the easiest ways to prevent fleas from completing their life cycle, which prevents adult fleas. But there are also several home remedies that can help with both prevention and eradication. Some of the most common homemade flea prevention remedies include:
Herbal flea spray. This spray is made with nontoxic ingredients you can get at the grocery store. You can make a large batch of this spray by mixing 1 gallon vinegar, 1/2 gallon of water, 1 cup of witch hazel, and 2 cups of lemon juice. Using a spray bottle, spray on carpets and upholstered surfaces after vacuuming, as you would an air freshener spray.
Salt. Salt can be used on carpeted areas to eliminate moisture. Take a generous amount of finely ground salt and sprinkle it all over the house. Leave it to rest for 1 to 2 days and then vacuum thoroughly. Finally, empty your vacuum directly into the trash can outside.
Baking soda. Like salt, baking soda can be used on carpeted and upholstered surfaces. After vacuuming, spread baking soda over your carpets and upholstered furniture, and then work it into the fabric using a brush. Then vacuum and immediately empty the contents into the trash can outside.
Lemon spray. Thinly slice a lemon and add it to a pint of water, peel and all. Bring this mixture to a boil and then let the solution sit overnight (you can store it in a mason jar). In the morning, pour the solution into a spray bottle and spray it in infested areas.
Diatomaceous earth. Diatomaceous earth is the powdered remains of diatoms or fossilized algae. It’s important to get food grade diatomaceous earth, since other forms can irritate skin, eyes, or lungs if inhaled.
This fine white powder is nontoxic to humans and animals, but can help eradicate insects. Diatomaceous earth can be sprinkled thinly in areas of the house where fleas take refuge. Leave it for at least two days and then vacuum thoroughly.
Other natural flea prevention remedies include sprinkling a mixture of rosemary with fennel, peppermint, wormwood, and rue in places with flea infestation or planting flea repellent plants like lavender, chrysanthemums, spearmint, and penny royal.
Preventing Fleas with Pesticides
For homeowners dealing with massive flea infestations, store-bought pesticides can get the fastest results. Options include a combination of liquid residual insecticides and IGR (insect growth regulators) to control the presence of adult fleas and prevent the larvae from turning into full-grown adults. Flea control aerosols are also available if you’re not comfortable mixing poisonous liquids yourself.
Check out our resources page for a list of pesticides we recommend. And if you have a flea problem you can’t handle yourself, contact a professional. They can recommend products and treatments based on your needs.