It is quite well known that only cave-dwellers and agricultural peoples have fleas. Nomadic peoples virtually never have fleas. They have lice instead.

In an area with an established flea population, it is relatively easy to kill the adults with insecticides - provided that the animal/host occupants can tolerate the treatment. Flea eggs, however, are almost completely invulnerable to any usable chemical attack.

Flea eggs do not "attach" to the animal, or even to bedding or other items, so when you move out, and shake things out as you go, the eggs are left behind. They may be hidden in carpet, crevices, or other places; but a "moving population" should take (mostly) only mature fleas with them. As long as one keeps moving until the current crop of adult fleas has finished dropping eggs, and moves fast enough that the eggs don't mature while you're still around, you should be relatively free of fleas.

It is reported that the eggs need a week or so to "mature," but can then lie dormant for as long as several years, so moving into an "infested" area is not a pleasant thing. The claim is that exhaled CO₂ triggers the hatching of dormant flea eggs, and the hatchlings can emerge and jump onto anything living within minutes, if not seconds.

If an infested area can be left with no animal presence for a period of a month or so, there will be no adult fleas left there. Introducing an animal of sufficient size will trigger rapid mass hatching, but the adult fleas are susceptible to a number of insecticides. If the hatching can be triggered "all at once" and the freshly hatched fleas "dispatched" before they mature enough to lay more eggs, an area can be made nearly flea free - for a time.

Most kinds of fleas have their preferred "hosts" and dog fleas don't commonly attack cats, or vice-versa; although there is some "flexibility" and most kinds of fleas seem willing to adopt humans as hosts if the population gets sufficiently dense. Cross species hosting is exceptionally common for humans and some kinds of rodents and other "wildlife" so rodent-proofing a place of residence is extremely important in getting rid of a flea population and preventing new ones from becoming established.

The most effective, in the long run, are the newer treatments that don't attempt to kill either the adult fleas or the eggs; but instead cause the the adults to drop only sterile eggs. The adult cycle is sufficiently short that the existing fleas will die of old age within a fairly short time, and interrupting the cycle so that no viable eggs are dropped is the most certain way of (eventually) getting rid of a flea population.

Or so I've been told by those who told me they know.

John