They eat Sweet Vegetable Cakes and you need to tranq them down with darts preferably. Aim for the soft part of the Achatina and not the shell part. Shooting its shell will take more darts to take down.
If you are considering breeding these, go slam your hand in a car door a few times. It will be much less painful. Literally one veggie cake per percent of growth....and it grows slow.. Digests roughly one point of food per second, so feed a cake about one for every 7 mins (during event boost) and it will gain one percent of growth.