Moths are harmless insects that are considered a pest and nuisance when they are in a house. The larval form of a moth is a caterpillar, which undergoes metamorphosis in a sequestered chrysalis. Moths differ from butterflies in their shorter, hairier antennae, nocturnal tendencies and resting position with the wings open, rather than closed. Knowing what causes a moth to come inside the house makes it easier to treat the issue and prevent further invasions.
Some moths eat dry foods derived from vegetable sources, especially grains. This moth enters the house through foodstuffs that have been contaminated or improperly cleaned at a point in harvesting and manufacturing. An infestation may also occur or spread within the stores, and the eggs are nearly undetectable in foods. These are commonly found in flour, cereals, rice, breads, birdseed and pet food, but their small bodies allow them to enter the smallest openings to spread the infestation.
Another common moth is the clothing moth. The larvae feed on natural fibres, such as cotton, wool, silk, fur, feathers and hair. Preferring dark, undisturbed areas, they are most often found in wardrobes, attics, storage containers, rugs or carpets that see little traffic. This insect enters the house on the occupant's clothing or in unclean purchases, such as an old fur or a second-hand sweater. Dead animals also attract the larvae. Adult clothes moths do not harm fabrics, but they will perpetuate the cycle of moths in the house.
Most moths are photophilous, meaning they are instinctively attracted to lights. No one knows exactly why moths are drawn to lights, but there are a few theories. Some scientists believe the moths are mistakenly using the light to navigate as they would with the moon. Still more scientists believe that the attraction to light is related to mating. Whatever the reason, moths tend to congregate on lights and move toward bright windows and doors, where they sneak in cracks or wait until the householder opens the door to move closer to the light source.
Some moths may enter a house simply because it is the safest place to be. A house is warm in the winter and cool in the summer. Moths can escape the rain or the snow with a sheltered place to sleep. There are fewer natural predators, because there are no frogs, bats or birds in the house. There is plenty of food lying around that they don't have to share with other moths. The things that make a household comfortable to human beings also makes it comfortable for moths.