In the Mallis Handbook of Pest Control there are comments about the ability of the Webbing Cloths Moth to fly, and I suspect that the Casemaking clothes moth may be similar. They state that it normally will be males that you see flying around, as the female may be so bulked up with her eggs that she is too heavy to fly comfortably, although it is possible she will and once she has deposited all of her eggs she then will more readily fly. And, of course, these moths generally avoid light, so they would not be the culprits if your customer finds moths flying around lamps inside or porch lights outside.
They go on to talk about the distance the moths may fly, and while these are not really strong fliers they have been found to move over 300 feet from a warehouse that was infested to nearby homes, and to find their way inside these homes. Obviously these moths occur outside of structures and find their own way inside to infest susceptible materials, so even with a weak flight they manage to get around on their own.
The clothes moths, like the carpet beetles, are scavengers and decomposers. Their "role" in nature is to feed on leftover animal materials, such as hair, feathers, dead insects, and to reduce them to powder that would then move back into the soil as nutrients for plants to use as food. They are very, very efficient at finding these kinds of food resources within a home. If there were any of these foods within those heating or cooling ducts I suppose the adult moths would detect them and could find a way into the ducts to deposit their eggs. The question, of course, is what could possibly be within the ducts that the moth larvae would eat, and for most systems it would seem that these ducts shouldn't have much in them in the way of hair or feathers or dead bugs. But, it is "possible" - maybe there is a break in the duct-work somewhere that allowed a bird or rodent to get in. Perhaps the filters are not in place and things are getting sucked in.
I would say that it is possible for the moths to GET into ducts if they detect a food source, but not to LIVE within the ducts just as a place to hang out.
Mr. Pest Control
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