A newly weaned and undersized kitten that I had not seen since it was born was apparently the only survivor of the birth process but turned up without any evidence of its mother's interest. It was able to adapt to eating solid food and was sturdy enough but had a pronounced tight swollen bulge on its neck/jaw area. I thought maybe it was a result of a bee sting. About a week later it drained and diminished. After another two days the kitten collapsed. The bulge had opened up, revealing a bot fly larva which I pulled out using tweezers. It was about 3/4 inch long. I'm guessing it was a deer bot (central New Jersey location). Unfortunately, ordinary flies were attracted to the drainage and open wound and deposited massive numbers of eggs. Many had already hatched into maggots and penetrated deeper than the reach of the bot fly larva. The kitten had lost too much body fluid and died from inability to sustain respiration while I was trying to eliminate the maggots.
That's truly horrible In the future you should always try to move sick animals to an AC room, if you have one, or keep them very clean from the beginning. Any swellings on kittens should be seen as serious, even if they appear to get better. Condolences, at least the little thing isn't suffering any more.