It is not necessary to have pets in the building in order to have fleas present. Since fleas can jump about 6″ vertically, they can easily hitch a ride on shoes, trousers, etc.
Many vacationers who may have been unaware of the few adult fleas present in their home, are often greeted and severely attacked by fleas upon their return. Fleas can be present even if the building has been vacant of animals and people for as long as 6 months. This situation can occur because of the potentially long pupal period, adults can live for months without food, and because fleas have not been removed via normal vacuuming. Also fleas are normally removed from the interior environment by taking up residence on the pets.
Fleas are typically found where animals sleep or frequent, including along their usual avenue of travel, because this is where eggs and adult fecal blood accumulate. Most larvae will be found in similar places but especially in areas with high moisture which is necessary for their survival. Pupae will be found in the same situations as larvae. Such places include both indoor and outdoor situations. Fleas are also found on other urban hosts such as rabbit, spotted skunk, opossum, occasionally rats, and cats.
Flea larvae die at relative humidities below 45% and above 95%, and hence, are rarely found outdoors in arid climates. Larvae fail to develop at temperatures below 55 F. and at or above 95 F.