Why Does My Pet Still Have Fleas?


This is one of the most common questions we get at Bell Veterinary Clinic. You have treated your pet with a recommended product and yet, you are still seeing fleas on your pet.

Most people (understandably) expect, that if they treat their pet for fleas, that they won’t ever see another flea. Sadly, this level of flea control is impossible to deliver for several reasons, but don’t give up hope, there is a way to eradicate fleas.

Re infestation is the reason that you see fleas after you have treated your pet. There is a continual, day long procession of fleas arriving on the pet. These newly arrived fleas die within 24 hours of contact with adulticide chemicals, but as an observant owner, you still notice the fleas. If you look carefully, you’ll see that some of the fleas are small (unfed), some are bigger (fed) and some are big and lethargic (dying). There is always a population mix of new arrivals, actively feeding fleas and sick, dying, and dead fleas on the pet.

So why does this happen?…Well, fleas are insects and as such, have an egg stage, a larval stage, a cocoon stage and a parasitic adult stage. Incidentally, adult fleas are the only stage found on the pet and they cannot survive off the pet once they have fed. The egg, larvae and cocoon are found in the pet’s environment (bedding, carpet, yard, etc.). Each female flea produces, on average, 30-50 eggs a day. The eggs hatch into larvae, which eventually become a cocoon after one to two weeks. The cocoon stage can survive happily in the environment for at least 6 months.

Inside the cocoon, the larval flea has become an adult flea (some people call these ground fleas) which will then hatch in response to nearby vibration (i.e. pet’s/humans moving about), they emerge from the cocoon and jump towards the stimulation to seek a host. The cocoon stage is the source of all your problems (and fleas) and unfortunately, pre emerged fleas in cocoons are extremely difficult to kill.

When fully developed, these pre emerged fleas hatch whenever a pet walks past so they continually appear on the pet. In effect, today’s fleas were last month’s flea eggs. Within 24 hours of arriving on the pet, the fleas have fed and the egg production cycle starts again.