Apparently, live purring maggots are being counted as meat. Every time I try to milk them, some get eaten.
When they are in the cage, nobody will touch them; but when they are taken out to be milked, people will eat them as meat. I have abundant food supplies in my dining room, so most dwarves go for the cooked meals. But if they happen to be carrying a maggot when they get hungry, they eat it.
I have seen maggots used as food several times now, and noticed them disappearing constantly. The first time I noticed it, I had told my animal trainer to tame an elephant that I had just caught. I had previously told my farmers to milk the maggots. One was on the ground after being milked, and instead of it being taken back to the cage, the animal trainer ran and picked it up, and fed it to the elephant.
The second time I noticed it, a hauler had just picked up a maggot, was about to take the 2 steps to the cage, and he decided he was hungry. He cancelled the hauling job to eat, and then I saw him carry the maggot to the table to eat it.
And then just now I told my farmer to milk the maggots, then locked all the doors to the room hoping to keep someone from eating them. The farmer was in the process of milking the maggot when he decided he was hungry. He just stopped and ate the maggot he was supposed to be milking in the workshop! Then he just grabbed another maggot and continued milking.
I've been catching a handful of purring maggots every winter (when the bats are inactive, plus my farmers can double as trappers), but I never get any more of them due to them being eaten every season when I try to milk them. I've probably caught 50 or more of them so far, yet my cage only has 9 left now.