Let me begin by saying my Veterinary Knowledge on geese is not so good since I am into dogs and cats treatment, but I have an opinion.
There is a worm that affects turkeys, found in the intermediate hosts that are worms(Nematodes easily found on the ground )picked from the ground.
The domestic fowl is also involved in this life cycle. The protozoa causing this disease is Histomonas Meleagridis. Worm called Heterakis gallinarum , that is regularly eaten by the Domestic fowl from the ground .
Often the disease is called the Blackhead Turkey Disease. You can read more about the disease from Wikipedia
Based on this argument you should implement the following effective control measure for your geese:
Dimetridazole can be used in the drinking and feeding troughs Cleaning premises and ensuring Bio Security measures are implemented in the Farm. Dead Birds should be buried or burnt after PM examination
I hope this partially answers your question Thanks Dr Joe
Thanks for your answer afriqnet, but it wasn't a question of disease but of diet. I want to know if geese eat bugs and beetles as part of their diet. It would also be interesting to know if they eat slugs and snails like ducks do.
Most geese feed on grass and lots of it but they will accidentally pick up the occasional creepy crawly and other small beasties. In this respect they're not as efficient as say hens in keeping bugs and pests under control. Geese are a traditional watch dog however and if not too tame will challenge human intruders, hissing and biting. They run away from foxes.