In the current version of the game, 40d, when setting animal traps with meat or fish, a dwarf will put an entire stack into the animal trap. The idea of a little cave spider devouring cow meat [9], which is enough for nine meals for a dwarf, is a bit mind-boggling. I think it would be better if animal traps were only loaded with one unit of meat or fish. Also, the eating of vermin by dwarfs makes collecting certain types of vermin, say purring maggots or cave spiders very difficult, which is a problem that I'm sure people are already aware of. I would suggest having the eating of vermin as something that could be allowed from the stocks screen, much like the selling of vermin as pets, or as something that could be activated from the vermin itself. Animals trapped in cages would have the default value for being eaten as set to "false" automatically, and, for unwanted vermin, the value could be set to true or the vermin dumped into some pit somewhere to free up traps. I think that would improve things quite a bit, and allow for the farming of cave spiders and purring maggots for silk, milk, pets, and exotic food.
Edit: Also, the milking of purring maggots needs work. In current version, a milker takes a live maggot from an animal trap and milks it, but then drops it on the ground instead of re-caging it. You can then assign the maggot to a built cage, but milkers cannot access it for milking from there. Maybe small animal cages could be implemented at some point.