If you see fleas on your untreated pet the chances are that there are many, many more lurking close by.
The adult fleas on an untreated pet will not only be taking a blood meal courtesy of your pet, but will also be laying eggs – up to 50 a day in fact. These tiny eggs are like grains of sand and they slide off your pet into your home. In as little as one day (or as long as 12 days), the egg hatches and out wriggles a flea larvae. About half a centimetre long (so still very hard to see) the larvae will hide in dark places such as within carpets or under furniture, or in the cracks and crevices of floorboards.
After a couple of weeks the larvae become cocooned. The cocoon is sticky and not always easily dislodged even by vacuuming. The cocoon protects the developing pupa until an adult flea is ready to emerge. That adult flea only comes out of the cocoon when there is a pet (or human) nearby to feed from. When that flea jumps onto your pet it will feed and 24 hours later will start to produce eggs, starting the lifecycle all over again.
There are a few things you need to take away from this to help you control fleas in your home and on your pet: