Black Rat: Black rats, also called roof rats, are agile rodents that often seek shelter indoors as temperatures begin to drop in September. They are excellent climbers and can enter homes through small openings, especially in attics or upper floors. Their search for food and warmth makes them more visible this time of year. Black rats can contaminate food, damage insulation, and chew on wires, which may lead to fire hazards.

Carpenter Ant: Carpenter ants are large black ants that become more active in late summer and early fall as they search for food and new nesting sites. They do not eat wood but excavate it to build their nests, which can weaken wooden structures over time. In September, colonies may send out winged ants to start new nests, making them more noticeable indoors and around homes. Their presence often indicates moisture problems or decaying wood in the structure.

Yellowjacket Wasp: Yellowjackets are aggressive wasps that are especially active in September. Their colonies reach peak size at this time, and food sources in nature become scarce, so they are more likely to invade outdoor gatherings, trash cans, and kitchens in search of sweets and proteins. Their stings are painful and can be dangerous for people with allergies. Yellowjackets often build nests underground or in wall voids, making them hard to spot until disturbed.

Boxelder Bug: Boxelder bugs are black and red insects that start gathering in large numbers on sunny walls and windows in September. As the weather cools, they look for warm places to spend the winter, often entering homes through cracks and gaps. While they do not bite or cause structural damage, their droppings can stain surfaces, and their presence in large numbers can be a nuisance.

Cluster Fly: Cluster flies are larger, slower-moving flies that begin to appear in homes in September as they seek sheltered places to overwinter. They often gather in attics, wall voids, and unused rooms, sometimes in large numbers. Unlike houseflies, cluster flies do not breed indoors or feed on garbage, but their presence can be bothersome, and dead flies can attract other pests.

Stink Bug: Stink bugs are shield-shaped insects that become more noticeable in September as they look for warm places to overwinter. They often gather on sunny sides of buildings and may enter homes through small openings. When disturbed or crushed, they release a strong, unpleasant odor. While they do not cause structural damage, they can damage garden plants and crops before moving indoors.

Earwig: Earwigs are small, brown insects with pincers on their rear. In September, they are often found in damp, cool areas like basements, bathrooms, and under mulch or debris outside. As outdoor conditions become less favorable, they may move indoors in search of moisture and shelter. Earwigs are mostly harmless to humans but can be alarming due to their appearance and tendency to gather in groups.