Cuttlebone for Isopods: A Simple Calcium Source

Cuttlebone is one of the simplest ways to give your isopods calcium. Isopods rebuild their hard exoskeleton every time they moult and harden it with calcium carbonate, so a calcium source belongs in every tub. A piece of cuttlebone left permanently in the enclosure is an easy, long-lasting way to keep that supply available. This guide explains what cuttlebone is, why it works, and exactly how to offer it.

You can pick up cuttlebone here, and our guide to calcium and supplements covers the wider picture.

What Is Cuttlebone?

Cuttlebone is the internal structure of a cuttlefish, a marine mollusc related to squid and octopus. Despite the name it isn't a true bone but a lightweight, porous structure made largely of calcium carbonate (aragonite), which the cuttlefish uses to control its buoyancy. That high calcium content is exactly what makes it so useful for isopods. It's been used as a calcium supplement in the pet bird and reptile world for decades, so it's cheap, widely available, and many keepers already have some to hand.

Why Cuttlebone Is Good for Isopods

The main draw is calcium, the mineral that hardens an isopod's exoskeleton. Cuttlebone is soft enough that isopods can graze on it directly, rasping away at the surface. It also contains trace minerals such as magnesium, zinc and iron.

A whole piece left in the enclosure works well because it stays put: it's always there, it lasts a long time, and you don't have to measure anything out. Keep a piece in every tub, whatever the species.

How to Offer Cuttlebone

The easiest method is simply to leave a piece of cuttlebone in the enclosure for the isopods to graze on as they like:

Rinse it first under running water to remove any surface debris.
Baking is optional. A short spell in a low oven (around 100°C for 20-30 minutes) helps sterilise it and makes it easier to snap, but it isn't essential.
Break off a piece by hand or with pliers, and place it on top of the substrate - laying it soft (porous) side up makes it easiest for the isopods to graze, and they'll often shelter under it too.

That's really all there is to it. Some keepers grind cuttlebone into a powder to dust onto food, but with a permanent whole piece available this generally isn't necessary - the isopods will help themselves. Keep an eye on the piece and replace it once it's been grazed down or starts to break up. As with anything, there's no need to overdo it: one accessible source is plenty.

Cuttlebone Alternatives

Cuttlebone isn't the only option, and many keepers offer a couple of calcium sources for variety:

Eggshells - free from your kitchen. Rinse, dry and crush them, then scatter into the enclosure. A simple extra beside a permanent source, though not a replacement for one.
Limestone - excellent, especially for Cubaris, which sellers place in limestone country. Use small crushed pieces; it provides calcium plus trace minerals.
Crushed shells (such as oyster shell) - calcium-rich and good value in bulk, offered crushed or as small pieces.
Powdered calcium supplements - convenient but pricier, and not really needed if you're offering a natural source.

If you'd rather avoid an animal-derived product, limestone is the one to choose: like cuttlebone it is calcium carbonate, and it is hard and long-lasting in the tub. Whatever you choose, the principle is the same: keep a calcium source available, don't over-supplement, and top it up as it is used.

Frequently Asked Questions

Can isopods eat cuttlebone?

Yes. Isopods graze cuttlebone directly, which makes it one of the easiest calcium sources to offer. Just leave a piece in the enclosure.

Do I need to prepare cuttlebone before adding it?

Minimal prep. Rinse it under water, optionally bake it briefly in a low oven to sterilise, then break off a piece and place it soft side up on the substrate. That's it.

How much cuttlebone do isopods need?

Just keep one accessible piece available and replace it when it's grazed down. There's no need to ration it or dust food with powder.

What are the best alternatives to cuttlebone?

Limestone (great for Cubaris, which sellers place in limestone country) and crushed oyster shell both work well as a permanent source, and crushed eggshell (rinsed and dried) as an extra beside one. Limestone is the one to choose if you'd prefer not to use an animal product.

Can you give isopods too much calcium?

Over-supplementing isn't helpful, but simply leaving cuttlebone available rarely causes problems. Offer one source rather than piling in several powders.