If they take stuff from the surface, a dubia roach colony is easy as well. Good calcium source, can be gut loaded just need about 80 - 85 degrees (I use an under tank heater) to breed, eat veggie scraps and the frass / waste bedding (rolled oats) also make great fertilizer.
A small / medium tote (5-10 gallon) with a ventilated lid, some egg cartons, heat source is really about all it needs aside from changing the bedding as needed. I have plenty and could easily separate out some breeding adults and some juveniles to grow up if anyone wants.
Fed the fish, scraped a couple tanks / filter cleanings this morning then got Shanghaied into moving medical equipment out of the wife's old clinic to move to the new one. Building changes hands tomorrow and wife had a busy couple weeks being short staffed and having to actually do medical stuff instead of management. Missed a few opportunities due to that, but it's done now.