Can I keep different isopods together? We get asked about cohabitation all the time. Here, we'll go through the pros, the cons, and the hows.
Pros
It looks good. Your enclosure gets more variety in size, color, and pattern.
I can't argue with this. Who wouldn't want a bin of live jellybeans? 🤪
It's simpler (?). You have fewer enclosures to deal with. If you keep all your isopods in one enclosure, you have fewer enclosures to worry about!
While this is true, I'd argue that keeping one mixed enclosure is often more complicated than keeping two separate species-only enclosures. There are tons of moving parts - different environmental needs, different breeding and growth rates, competition, etc. Cohabbing introduces tons of complications that aren't a problem with species-only bins.
It's more natural. Wild isopods don't exist in a vacuum. Isopods are often found in places where there are other animals, and other isopods! Keeping different kinds of isopods together allows us to observe interactions between the different kinds. Species only bins are unnatural.
Another thing that's natural is competition. If you are alright with your rarer isopods being outcompeted by others, this should not be a problem. However, if you want your Rubber Duckies to thrive in a bin with Cubaris murina, I wouldn't cohab. Competition is natural, and you should expect a species or two to dominate your enclosure in the long run.
Cons
Hybridization (?). This is a common fear that is likely a carryover from other exotic pet communities. Hybridization is a taboo in most communities, but this is not a risk in isopod-keeping. Successful breeding between different species has not been recorded.
There is a real con here, though. Say you start with some Cubaris murina and some Cubaris sp. Rubber Duckies. Soon, you'll have dozens of murinas and the same number of RDs. The male murinas will constantly attempt to breed with your RDs. You won't have any hybrids, but you will have very stressed RD females.
Predation. This is a legitimate con with some isopods. Aggressive, protein-hungry isopods are opportunistic predators. A molting isopod could fall prey to hungry neighbors.
Be extra careful when trying to cohab species like Porcellio laevis, Porcellio scaber, and Porcellio ornatus.
Competition. Space and food are limited. This becomes immediately apparent once your isopods start breeding. The fastest breeding species will eventually outnumber and slowly outcompete the other isopods.
This can be slowed down if you periodically rebalance your enclosure population. Competition also isn't a problem if you don't mind your enclosure slowly becoming a single-species enclosure.
How To Do It
New Keepers. You're new to keeping isopods, but you are intent on keeping a mixed enclosure. I recommend a mixed morph enclosure. Keep the same species, but mix morphs! You get different color morphs, but you only have to worry about the needs of one species. Candidates here are Porcellionides pruinosus mixes, Porcellio laevis mixes, and Porcellio scaber mixes.
Experienced Keepers. Sky's the limit. When you build up experience in isopod-keeping, you invariably also build up a huge population of isopods. Take a few specimens from your species-only bins and build little worlds that can accommodate all their needs! Your prior experience will come in handy when husbandry problems pop up.