Open this one over a sink and dampen the powder before you start mixing it into anything. Dry guano makes dust, and the dust is the part worth taking seriously. The fungus behind that caution, Histoplasma capsulatum, grows in soil enriched by bird and bat droppings and is commonest in North and Central America. It is not present in British bats or in the British environment, which is reassuring right up until you remember that commercially traded guano is mined from caves in the parts of the world where it does live. In 2024 a case report in Open Forum Infectious Diseases described two fatal infections in cannabis growers, one of whom had bought his bat guano from an online store, and its authors recommended that products of this kind be labelled with a warning and instructions for safe use. So: wet it down, do not tip or sweep it dry, wear a mask if you are working with a quantity of it, and wash your hands afterwards. We have not found anything that puts a number on the risk from a 50g bag and inventing one would not help you. With that dealt with, what it is for. Guano is a nitrogen, phosphorus and potassium source, and those figures vary enormously between one deposit and the next and between insect-eating and fruit-eating bats, so any printed analysis should be read as indicative and not as a spec. Guano is often sold as composted over hundreds of years. Cave deposits do reach great age, but the process is not composting and age is not a quality mark: in damp caves it strips the organic content out instead of concentrating it. Why isopod keepers use it The reasoning is ecological. Inside a cave, bat droppings are one of the few substantial energy inputs into a system with almost no plant material arriving, and the invertebrate life tracks that. One survey in the Levant found isopods made up 19.5 per cent of all arthropods in caves holding fruit-bat colonies, against 1.8 per cent in caves with no bats at all. Isopods in the family Armadillidae, which is the family Cubaris sits in, have been recorded feeding directly on fresh and mouldering bat droppings in Philippine caves. What does not exist is a feeding study on any of the premium Cubaris actually sold in the hobby, and Zimmer's 2002 review of isopod nutrition, still the standard one, does not mention guano anywhere. Offer it as a plausible enrichment for the premium Cubaris, not as something they require. Our guide to how often to use bat guano for isopods covers the schedule side, with thin surface applications every two to four weeks at most. Use it sparingly, because it is high in nitrogen and nitrogen accumulates in a closed tub. Roughly a teaspoon mixed thoroughly through five litres of substrate at setup, or for an established enclosure, damp a very small amount and work it into the surface instead of dusting it on dry. It is a supplement and not a food: leaf litter and rotten wood still do the feeding, and it does nothing for calcium, so keep a cuttlebone in regardless. Between uses, keep it sealed, cool and dry. A 50g bag mixed at that rate goes a very long way, which is the other argument for restraint.
