Not all pest problems announce themselves with a swarm or a mouse scurrying across the floor. The earliest signs of an infestation are often subtle and easy to miss. Unusual smells, faint sounds, or mysterious stains could signal that unwanted visitors have taken up residence.

Here are seven warning signs — and what they might mean.

1. A Musty or Oily Smell That Won't Go Away

A persistent, musty odor that lingers despite cleaning could indicate rodents or cockroaches. Rodents leave behind a distinctive urine-like scent in their nesting areas, while roaches produce a greasy, lingering odor as their numbers increase.

2. Scratching or Skittering Sounds in the Walls

Do you hear noises at night? Scratching, tapping, or movement in your walls or ceiling might indicate mice, rats, or squirrels. These nocturnal pests are most active when your house is quiet.

3. Mysterious Droppings or Debris

Droppings are a telltale sign of pest activity — though they can be tricky to identify. Rodent droppings look like dark grains of rice, while insect droppings appear as smaller, pepper-like specks. Watch also for shredded paper or insulation, which could indicate nearby nesting.

4. Grease Marks or Rub Lines

Rodents typically follow the same paths repeatedly, leaving greasy rub marks along baseboards, pipes, or walls. Dark, dusty-looking smears in these areas warrant closer inspection.

5. Chewed Food Packaging or Wiring

Perhaps the most concerning sign is gnawed food containers or electrical wires. Rodents' teeth grow continuously, compelling them to chew on virtually anything — from cereal boxes to insulation and wiring — creating serious safety hazards.

6. Sudden Spike in Insect Sightings

While seeing an occasional spider or fly is normal, a sudden increase in ants, roaches, or flying insects — particularly in kitchens or bathrooms — may indicate a nearby nest. These pests are naturally drawn to moisture and food debris.