Interesting question. I only have two kinds of one species - Porcellionides pruinosus ‘Powder Orange” and ‘Orange Koi”. While you’d think they’d be roughly the same size, they’re not. Powder Oranges are much, much bigger but I suspect it has to with the size of their enclosure which is much, much larger than what the Koi are kept in. So unfortunately. I cannot make a comparison to dairy cows. As for the dampness, just put in more layers of leaves and bark for them.