Cleanup crews are a mix of springtails and isopods. Springtails eat mold, and isopods eat material itself, such as feeder remains/mantid frass (poop)/and other wastes. For either/both you will need a substrate for them to live/burrow into as needed and for moisture retention.
I personally use about 3/4" or so of sphagnum peat moss, coconut fiber, or similar (I use sphagnum peat moss exclusively now as $15 bought a
huge bale at my garden center that will last a lifetime and has had no ill-effects after a year of use). A substrate soaks up any excess moisture and releases it slowly for your mantids, looks nice, and keeps the habitat looking clean as well.
I found in order to keep the isopods moist (as they have to be damp to breath) it is a bit of a balancing act on humidity to keep them alive and prevent mold growth (if ventilation is a issue). The springtails take care of the mold; however, excess moisture can lead to bacterial problems too. To prevent those problems though, cross-ventilation along a side near the bottom (one side is good enough) and at the very top of the habitat, will keep problems to a minimum even if the habitat is over misted.
I noticed several of my mantids liked to attack the isopods when they moved around on sticks, but ignore them completely when they stay on the substrate. For 32oz deli cups it seems 3-4 isopods is about the right amount to keep them busy cleaning, and from annoying mantids.
Personally I keep both springtails (a big colony) and various isopod habitats primary as pets now, and the springtails as occasional feeders for some small mantid species. I find removing larger pieces of feeder leftovers occasionally enough cleaning, anything else is for human benefit only, and hasn't affected my mantids.
Springtails are great at cleaning mold if you do excess watering, and do help break down the feeder remains (perhaps as they decay/mold) as it's said they only eat mold. Anyway their population will grow/shrink as food becomes available so that is of no concern (as long as they do not dry out and die off).
They tend to only stay in the habitats (food/water) and should dry up and die off if they do leave the tank. I kept them in a fiberglass mesh tank (solid bottom) but mesh sides they could easily escape from and never had any problems with loose ones even then in that mantid habitat. That said they live in dirt, and even appear by their own means in potted house plants kept only inside even from seed/starts - so they are all around even if you don't have/had/keep them anyway to some extent.
