Gape worms are found in the windpipe of the bird where they cause irritation. In severe infestations they can block the windpipe and choke the bird to death. Birds are seen snicking and head shaking.
They get infected by picking up the eggs from the ground or by eating infected earth worms. Earth worms can live for up to 7 years so can remain a reservoir for infection for a long time. Carrion birds are also a major carrier of gape worms.
Routine worming will keep the gape worm under control. Birds will build up immunity over time, but when birds come in to lay, this immunity will weaken, so do not forget to worm laying birds on a regular basis.