“We just moved into this house. It is overrun with fleas and they are biting us! We don’t have any pets and the place was vacant for five months before we moved in. Where are these fleas coming from and how can we get rid of them?” This situation often occurs when new owners or tenants move into living quarters where the previous tenants kept pets. An understanding of flea biology provides the explanation.
Adult fleas live on the host animal where they use their piercing-sucking mouthparts to suck blood, but immature fleas, known as larvae, live on the ground/floor in areas where infested animals spend time resting. When adult fleas lay eggs, the eggs drop from the animal onto the floor or bedding area where they hatch into legless, white, worm-like larvae. Flea larvae do not suck blood; they feed on the feces of adult fleas along with dander and dried specks of blood that drop from the animal into the bedding area.
Fully-grown flea larvae pupate by forming a silken cocoon, much like a moth caterpillar. Under normal conditions they emerge as adult fleas in around one or two weeks and immediately hop onto the first available host. But if fleas that have developed to adulthood inside their cocoons do not sense the presence of a warm-blooded host, they will remain inside the cocoon and not emerge until they know a host is present. They can survive in this waiting state for many months, even as long as one year.
This explains what happened in the above scenario. When the previous owners moved, they took their pets and all the adult fleas that were on those pets with them, leaving the immature fleas behind. While the house was vacant, all these immature fleas developed into adults, but they did not emerge from their cocoons because they did not sense the presence of a host. Now that the home is again occupied by a warm-blooded animal the fleas are emerging from their cocoons and looking for a blood meal. They would prefer a nice dog or cat, or even a racoon or possum, but in the absence of these they will readily bite people.
How do the fleas know when a suitable host is present? How do they know when to emerge from their cocoon? They can sense the presence of a host in several ways, including body heat, carbon dioxide in exhaled breath, and especially from vibrations due to movement. This is why thorough vacuuming is such an important first step in controlling fleas in these situations. Not only does vacuuming physically remove many fleas and their larval food, but the vibrations and movement triggers waiting adults to go ahead and emerge, making them more susceptible to other control measures.
See Extension Publication 2597, Control Fleas on Your Pet, in Your House, and in Your Yard, for more information on flea control.
Thanks to Extension Medical and Veterinary Entomology Specialist, Dr. Goddard for his input and assistance with this article
Blake Layton, Extension Entomology Specialist, Mississippi State University Extension Service. The information given here is for educational purposes only. Always read and follow current label directions. Specific commercial products are mentioned as examples only and reference to specific products or trade names is made with the understanding that no discrimination is intended to other products that may also be suitable and appropriately labeled.
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