Oct 07, 2016 - 10:53 AM
Thats very difficult to say. Flea pupae can remain in a dormant state for up to a year. However, since you have been in the structure all of this time, I would suspect that if the fleas were active, then you would know by now. However, the only way to really know is to turn on the furnace and see what happens.
Oct 10, 2016 - 10:14 AM
In most cases, unless there were animals living in the ducts, the chance of flea pupae being in the ductwork is remote. If there are flea pupae there, then turning on the heat in most cases would either cause them to pupate and the adults emerge, or it would potentially kill the pupae (by drying it out). In order for flea pupae to be anywhere, there normally has to be all of the life stages, eggs, larvae, pupae and adults. The eggs and larvae won't be there unless there are adults present, pupae won't be there unless there are larvae present. Basically there has to be propogation going on for fleas to survive and continue to survive. This requires all of the life stages and a host - for a blood meal.