When a roof is newly thatched, whether with straw or reeds, thousands of grey- brown moth caterpillars may suddenly appear in the house.
In the wild these larvae live on grasses and reeds, and they reach the house in the thatching material. It is nearly always the fully grown larvae which appear in this way, as they wander out of the roof in the autumn to find a suitable place to spend the winter.
Occasionally they gnaw their way into various materials where they re- treat for the winter, and then pupate in the following spring and emerge as moths. The adult moths will not lay eggs again in the thatch, so the owner of the house experiences only a single generation and there is usually no need to take drastic action.