Cockroaches appearing at night — Amsterdam, Noord-Holland

Seeing cockroaches scurry when you turn on a light at night usually indicates an established infestation — for every roach you see, dozens more may be hiding in wall voids, behind appliances, and inside cabinetry. German cockroaches (the most common indoor species) reproduce rapidly: a single female can produce hundreds of offspring in a year. Over-the-counter sprays repel roaches from treated surfaces but rarely eliminate the nest. A pest control technician uses gel baits, insect growth regulators, and targeted crack-and-crevice treatments that roaches carry back to their harborage, collapsing the colony from the inside.