An often overlooked portion of the diet of isopods is their need for calcium. After all, where is a little critter than munches on leaves getting calcium from anyway? Isopods have a very high calcium content in their bodies, so much so that keepers don’t even have to dust them with extra calcium when offering them as feeders to reptiles. Without a good source of calcium, isopod cultures wane over time, with an eventual and inevitable crash of the entire culture. Without calcium, the isopods weaken and cannot breed, grow, reproduce correctly, and have increased rates of failed shedding.
The calcium content varies by species; the armored genus of Armadillidium is widely thought to have the highest calcium content of isopods. However, the giant Porcellio species hailing from Spain have a particularly keen appetite for calcium; they may strip an entire cuttlebone in a matter of days. This is most likely due to their size and their heavily armored appearance, as well as many Spanish Porcellio are native to limestone cliffs.
Where do wild isopods get calcium? Aside from the trace amount of calcium that is available in wood and leaf litter, the detrivore aspect of isopods allows them to derive it from a variety of sources. They strip carcasses and geological sources alike, processing bones, shells, and soil.
The easiest and cheapest way to provide calcium is to just cook frequently. Egg shells are an abundant source for calcium that isopods munch on. The shells are so dense that isopods will much on them for months before eating them completely. Many people assume that egg shells need to be sterilized; this is incorrect. The shells don’t even need to be washed, the egg goo leftover is filled with protein that the isopods enjoy, and salmonella is not a concern for the health of arthropods. The only threat that shells pose to isopods is that babies may become trapped in the thick goo. To avoid this, the shells can be air dried, then crushed before offering. Some people even choose to grind the shells into a powder so they can better monitor the amount of shells in the enclosure. Egg shells can also be placed in enclosures whole, on their side or open side down, and small isopods will use it as a hide.
The next best item to offer as a calcium source is cuttlebone. Cuttlebone (not cuddle- though adorable, cuttlefish are very aggressive animals) is derived from the cuttlefish, a cephalopod closely related to octopus. Cuttlebone is harvested especially for captive birds as a calcium source; it is soft and easy for animals to scrape up and consume. Isopods consume cuttlebone much more quickly than other sources because it is much softer. Cuttlebone, being derived from a sea animal, smells strongly of fish when first unpackaged. While some people may find this offensive, the isopods love it and will swarm the cuttlebone when it is unpackaged! Cuttlebone can be sourced in the avian section of pet stores or online from retailers in bulk.
Limestone is a source that is high in calcium as well. Limestone is readily available at garden centers in pelletized form, and is frequently added to potting soils for the benefit of plants. Many giant Porcellio species such as Porcellio expansus are native to Spanish limestone cliffs, and Cubaris species are native to Thai limestone caves so may particularly benefit from being offered limestone. Limestone can be offered as pellets, a ground additive, or even whole rocks. It is fun to offer the entire rock, because the isopods will slowly burrow into it and use it as a hide. Limestone can be sourced from garden centers and online.
Bones, antlers, shells and other animal products are also rising in popularity as a source of calcium. Due to their size and density, it may take years for the isopods to break these down. They may be offered as a whole bone, or for a more space efficient method, can be broken or sawed into smaller segments. Bones and antlers are somewhat hollow, so as the insides are exposed, the isopods will also use them as a hiding area. Bones can be sourced from leftovers from human consumption, at a pet store, or even a butcher shop. If sourcing bones from outdoors, please be cautious of possible bacteria and parasites for your own safety.
Another item that keepers inquire about using as a calcium source is powdered calcium offered for reptiles. Isopods can certainly use powdered calcium (or, even calcium tablets) as a source, but we don’t recommend this only because it is a rather expensive method to offer calcium. Powdered and calcium tablets also wash away with mistings, making it difficult to monitor if isopods need additional calcium.
Calcium is an important aspect of the diet of any species of isopod. While some may need it more than others, a source should be constantly available for any culture. There are many ways to offer it to the animals, depending on the keeper’s budget and resources.