Rescued, spayed female. Her belly is HUGE, as if she's pregnant with TWO litters! Has been to the vet several times, but I'm unable to get a stool specimen (I have 5 other kitties, and she will not use another litter box 🙄). I also see blood in box, but don't know which cat it is, but is likely hers. These small black "gnat-like" flies hatch from the litter box. I Googled "worms that hatch" and got NOTHING. PLEASE help! I've never seen anything like this in my 50 years of having cats!