What can insects use to gain access to buildings at the floor level?

Insects can gain access to buildings at the floor level through various pathways, and one significant method involves using pipes that go through floors and walls. These pipes create openings that can serve as entry points for pests such as cockroaches and ants, which are known to exploit even the smallest gaps in search of food, shelter, or moisture.

The other options focus on more limited access points. Ventilation systems can be a route for some pests, but they are not the primary means by which insects typically enter a building at floor level. Similarly, windows and light fixtures are generally above the floor level and are not as common for insects seeking entry close to the ground. Therefore, pipes through floors and walls represent a more universal and practical entry point for various types of insects.