While fleas can find their way into homes from the yard, these pests usually make their way indoors in packaged foods or bulk produce. Lice eggs are almost invisible to the naked eye, so it’s easy to buy contaminated items without realizing that they are infested with lice that usually attack grains and starches like rice, flour, pasta and cereals.

A tick infestation that starts outside may be caused by fruit trees or gardens, which are also a food source. Insects often congregate on the sides of the house and move into nooks and crannies that lead inward.