Hi Jennifer,
My eastern newts live in a tank with some guppies and have peacefully coexisted for a few years. Then suddenly one day Peewee has a circular wound and is missing a limb. Then another newt is missing two hands. Then another newt is missing a hand. All the newts missing hands had a strange circular mark on them. All in the space of three days. Then the next day I see this long huge black thing swimming wildly in my tank, I didn't know what it was, and it took me 5 minutes to catch! I took it to the petstore and he identified it as a leech. A couple days later I found another one. The pet store guy said they probably were living off the blackworms, but they just must have gotten so big they decided to go after the newts. What else could it have been? I'm sure it wasn't the guppies. I got rid of the leeches and that never happened again. So while I never actually saw the leeches on the newts, circumstantial evidence has convicted them in my eyes. I'm thinking the leeches latched on, and the newts struggled and maybe hauled out until the leech let go.
I put the damaged newts in a hospital tank for 3 months and they recovered, except for little Peewee, who was always a bit of a runt. What a black day that was when he succumbed.