2/19/2021: On Cubaris and Limestone
One of the most frequently asked things about Cubaris care is whether or not limestone, which has been touted as critical to Cubaris health, is necessary. Many are surprised to find that I do not use limestone for any of my Cubaris, from sp. “Rubber Ducky” to sp. “White Tiger”. This is because it is entirely unnecessary.
It seems at some point the association of these species with limestone caves (though not all are cave-dwellers) spurred the idea that it was somehow necessary for them, with the most ludicrous notion being that they fed on it. This is at worst misinformation used to sell a product and at best a fundamental misunderstanding of detritivore behavior.
Although strong enough to be felt on human skin, isopod mandibles are nowhere near powerful enough to actively consume rock. On the off chance that any tiny microparticles are digested accidentally during what seems to be direct feeding, they are no-doubt passed through the digestive system unaltered. It’s standard practice that organisms tend to deal intrusive inorganic matter as some sort of bodily intrusion. Rather, any “rock-feeding” behavior is a misinterpretation of what isopods may be doing on these surfaces.
Aquarists are familiar with the “algae-eating” behavior of many sucker-mouthed fishes and snails, evidenced by lines of clearly-grazed algae on aquarium walls. However, the extent of these colonies of micro organisms covering such surfaces (called periphyton) is not necessarily limited to aquatic ecosystems.
In terrestrial ecosystems, it is well-documented that many detritivores are, in fact, feeding on micro organisms found on the immediate surfaces of these materials. This is extremely well-documented in cockroaches (more detail can be found in Cockroaches: Ecology, Behavior, and Natural History ) and certainly applies to many other detritivores. This is why well-rotted leaves and wood are preferred; they are the most palatable, have had their chemical structure changed by microorganisms (and in moistened leaves have active colonies of these organisms present), and thus contain the most accessible nutrition. The amount of rot time varies depending on the material; for a simple comparison, the saponins found in maple leaves degrade very quickly once the leaves have left the tree and are thus eaten very quickly. The tannins found in oaks take much longer to degrade and thus fresh leaves are extremely unpalatable, but once decomposed the greater bulk and mass of the leaf makes it highly desirable.
So how does this apply to cave Cubaris? Well, think of the wet walls of a limestone cave as you would a slimy boulder in a stream (or, even less glamorously, the area under a leaky pipe in your basement). The water trickling over it provides an ideal surface for microorganisms to enumerate. Unlike ecosystems that are exposed to light and extensive nutrients from outside sources, cave ecosystems have fewer of these inputs (at least where bats are absent) so the growth is less abundant, but regardless ever-present. This is what the isopods are truly feeding on in these systems.
Sometimes other material may enter caves by similar processes that led to its colonization by isopods, and these organic influxes are no doubt utilized as well. Consider that a single leaf swept into an otherwise desolate cave could provide enough energy for a female isopod to produce many more litters than she usually would on her periphyton diet; it would be extremely favored for these cave species to exploit any boom in resources and thus there is some degree of flexibility in their dietary capabilities.
Long story short: stop feeding your animals rocks. Unless they’re birds, you’re more likely to cause problems by accidentally crushing them during maintenance than to give them actual nutrition. For cave-dwelling species that tangibly prefer smooth surfaces, use bark.