Snail and hermit lifespans

[daplatapus]

When I set up my tank almost 2 years ago, I put in bunch of hermits and snail and over that 1st year I added more, including a selection of snails and blue legged hermits. I've recently noticed I have no hermits left that I can see and maybe a half dozen or so snails. What's the lifespan of these things anyway? Do you guys have an annual replacement regimen or do I have an aquarium mystery on my hands? Alien abduction maybe?

I've had no problem keeping anything else, all my shrimp seem healthy, good pod population, I've always battled algae so I doubt they're starving... not too sure. Thoughts?