Clean-up Crew - A Myth

For those who describe snails and shrimp as "clean-up crew", here's another side to the story as far as nerite snails are concerned. Aside from the white dots (eggs) accumulating exponentially recently around the tank decor and walls, here's a photo of what one of the nerites has produced since Wed's water change, so I'll be doing another water change later on today. The male is in the photo - he's not guilty. The guilty party is the female who's been on the wood above and producing droppings almost constantly - and that's not all as a tetra has been sitting underneath and catching many of the droppings. 

 

In my case, I had the tiger orange nerite for over a year before I got the other snail. Not a single egg was laid during this time.
I then got a red waigiensis. For several months, nothing happened and I assumed/hoped I had two males. Then I noticed the white 'sesame seed' type eggs but, even then, assumed it was the white grains of sand which kept getting stuck on the wood due to being displaced during water changes. It was only after a while I realised that they might be eggs, confirmed by Sue who had kept nerites for years.
Although the eggs were initially only on the wood, which is where the female spends most of her time, I was only ever 95% sure they were hers - it might have been that the tiger orange snail only started laying eggs after the two of them "got together". However, this week, she was perched on top of the filter and I saw some eggs drop down - which definitively sealed the case for me that she was the egg-layer as I'd never actually seen them in the process of being laid.

Edited to add: I have seen photos on the www of how males and females can be differentiated but, despite examining their undersides, I find it absolutely impossible to tell. One has a pale coloured underside, the other dark, but otherwise they look identical to me.

Some snails are easy to sex - apple snails for example - but others can only be sexed when you catch them actually laying eggs.

I had two of one type of nerite and obviously one male and one female. They laid more eggs that I'd ever seen including all over the tank walls. Those were easy to remove, the ones on the decor weren't. I also separated them, one in the big tank and one in the betta's tank.

I think mine were "at it" overnight, judging by additional eggs and the fact they were cuddled up together behind the heater this morning (the latter being quite cute).