Thermobia domestica historically came from the dry litter community, living outdoors and feeding upon leaf litter and dead vegetation.  However, after adapting themselves to living indoors, their diet has changed.  In fact, the firebrat's preference for starches and carbohydrates may have helped give it its nickname. (Ordish 1960)  This insect is likely found around bakery ovens, stoves, and other warm situations where starchy or sugary foodstuffs might be found.  They are known to come out from their warm hiding places at night to feed on kitchen scraps that may have been left behind from human activities. (Lanham 1964)

They prefer protein, such as insect carcasses, to starch, the starchy substances indoors tend to be readily consumed by firebrats.  They will feed on the binding of books, the glue of wallpaper, clothes, and other items where starch sizing may be found.  These feeding habits in particular are one of the main reasons firebrats are considered pests.  Their damage to books, wallpaper, and the like can be extensive, causing many small holes from their chewing or their feces.  The silverfish, firebrat's caustic cousin, is know to cause more damage in the household, however. (Ordish 1960)

Water uptake and retention is important in all insects due to their exoskeleton, and they exhibit a waxy cuticle to aid in osmoregulation. (Hickman et al. 2009) In Thermobia domestica water is taken up by cutaneous pores in the exoskeleton, or through the anus.  Interestingly, these insects cease water uptake during the late stages of molting. (Davies 1988)

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