How big are flea larvae?

what a flea larva looks like under a microscope


Img 1 Cat flea larva under a microscope (1 mm measurement scale on the right).


Newly hatched flea larvae are 2 mm long. When fully grown, they’re 4-5 mm long, and 0.5 mm thick. The larval body is long and slender, like a worm or maggot. Prior to pupating, the body slightly shorten in length.


Larval Instars & Growth

Flea larvae develop through three stages, becoming 1st, 2nd, and 3rd instars. They molt once between each stage. Through this process, the larvae shed their outer cuticle to allow for growth. As a result, each instar is progressively larger in size.

Flea Larvae Size

Flea larvae have thin, worm-like bodies. Upon hatching from eggs, first instars measure about two millimeters in length. When they’re fully grown, third instars are four to five millimeters long, and 0.5 millimeters wide. Before pupation, third instars will slightly shorten in length.

Larval flea in dog bed

Vid 1 Video of a cat flea larva on a dog bed. See the pointing finger for a size comparison.

Size Comparisons

For comparison, an average piece of medium grain rice is 5 mm long, a sharpened #2 pencil’s tip is around 1 mm, and dimes have diameters of 17.9 mm. So, while cat flea larvae are very small, they’re still big enough to be seen by the naked eye.

flea larvae are big enough to see


Img 2 Comparison of the size of a cat flea larva to the tip of a sharp #2 pencil.


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  • Cathy August 13, 2017, 11:09 am

    Call my problem stems from a kitten that was given to me approximately 4 weeks ago I seen that she had fleas and I gave her a Dawn dish soap bath because I had no money to get the flea dip. I gave it to somebody that could take care of her and get her the help that she needed to be flea free. But I ended up having tons of fleas in my apartment that has all hardwood floors and my. I have flea bomb my apartment twice in seven days have washed my clothes twice and not let anything get on the floor hanging most of what I can up. I have no vacuum nor do I have a handheld. Please give me some advice on trying to get rid of these nasty things once and for all I’m still getting flea bitten. I have fears that they are in my bed and on my chair that I always sit on. Along with your apartment manager and myself we are trying to eradicate the problem we have done other treatments as well spray ons repellents. Was wondering if covering my bed wood plastic and my chair with plastic they have both been treated as I said with insecticide sprays or I should say bombs if there is anything else that you could suggest to me I would greatly appreciate it thank you so much for reading my note and I do hope to hear from you soon Kathy

    • Adam Retzer September 29, 2017, 12:29 pm

      Without the cat, the fleas should go away on their own in time. It often takes around 8 weeks, but may be a bit longer since you say your infestation was severe. Vacuuming regularly is one of the best ways to speed up the eradication process. Perhaps you can borrow a vacuum from someone?

      Luckily the fleas probably aren’t in your bed or on your chair. They can only jump to around the height of a human ankle. Sometimes they get into beds if infested animals sleep there, or if sheets are hanging low to the ground. Ensure your sheets are tucked in so there is no route onto your bed.

      Spray-on insect repellents are effective against preventing flea bites while you wait for the infestation to end. To prevent bites, it can also help to wear socks and pants, tucking the pant legs into your socks.

      I apologize I wasn’t able to respond to this earlier. I hope this reply can still provide some help.