Stage II of watching a process unfold:
Henry (my betta), didn't show much interest in my black nerite. First two weeks the nerite moved around the 10 gallon at will. He then began hiding in the driftwood, not seen much. I didn't think much of it and bought nerite 2/tiger nerite.
Put him in the tank at night and the exact spot he was before I went to bed was the same in the morning with Henry glued to him.
Henry had tore his fin on something so I opted to take things out of the tank and put Henry in a separate tank.
Rearranged the 10 gallon with only plants and a few polished rocks.
Henry was out of the tank for 5 days. Nerite was doing a wonderful job with diatoms/algae.
I put Henry in again and he was relentless. Finally, he looked like he grabbed the snail and shook it, then head butting while it was on the ground.
No worries, I got the nerite out.
Henry did not show this behavior with the black nerite, but the tiger was a different story.
I just purchased a tank divider and my plan is to put the snails on one side, then when they run low on food to switch with Henry.
I definitely will not trust Henry with any other tank mate at this time. For some reason the red tiger really triggered Henry.

Oh gosh, at least the snail is okay! I remember a while back when I had a nerite in with my old betta, King. One day I caught him eating something/messing with something. I don't know if the snail died and just fell out of his shell or if my betta got him out but sure enough he was biting/eating the snail and I was just standing there like "oh my god please stop DON'T EAT GARY!" and well, it's safe to say that was the last time I had a snail (or any tank mates) with my guy, King! Maybe your guy doesn't like his snail friends either!

I’ve posted in another forum about my fish and nerites. Some betta’s, I’ve found anyway, have a sensitivity to reddish coloured snails. When I added one to my halfmoons tank he constantly flared at it ripping one of his fins. I bought him another plain zebra nerite and although he still periodically flares at both of his snails, he’s much calmer about it. I took the snail out and added it to another betta tank. Now the betta in that tank hates both the zebra and red nerite. He does flare a lot at both of them and spends a lot of time hovering over them, showing how big he is, he even tried to fit them in his mouth. Lol. I don’t worry about him, he’s been doing it for months and because he’s a plakat, his fins are less prone to ripping. Also because he’s in a tank with shrimp, the snails have more places to explore where my boy can’t see them. Actually, my poor boy looks depressed and bored when he can’t find them. Lol. I added another snail to my other plakat’s tank, a little red, it looks like a ladybug. He’s flares more at that one than his zebra snail and that snail actually hides more than the zebra. So I definitely think red is a colour that betta’s can see, and the snails themselves are invaders of the tanks, so it makes sense that the fish will sometimes have a bad reaction to them.

that makes sense to me because he showed no interest in the black nerite. I love how efficient they are with keeping the tank clean so still may use the tank divider when they arrive. The red color of the tiger matches my gravel, so ignorant me didn't think he would notice him. Wrong! It honestly looked like when a dog gets a rabbit. Didn't know a betta could do that.

Lol. I know exactly what you mean, they go nuts! My half moon always knew where that red one was. Even when it was hiding in between the Anubius on the driftwood. He would just sit there staring at it waiting for it to move. Smart fish. I agree, I love my nerites and they are great cleaners. They are great tank mates for betta’s, just not the poor red ones. All my snails have names. One pair is Cheech and Chong. Lol.

i let someone else name my black nerite. Yep, you got it ..... Gary! :)