Dried Calciworms (Black Soldier Fly Larvae)

Calciworms - also known as soldier fly larvae - are the dried larvae of the black soldier fly (Hermetia illucens), and they're one of the most useful supplementary foods you can keep on the shelf for invertebrates. What sets them apart from mealworms and other dried feeders is calcium - gram for gram they carry many times more of it, along with around 40% protein. That combination of high protein and high calcium in a single food is unusual, and it's exactly what a lot of our animals need to grow, moult, and breed well.

At a Glance

• What it is: Dried black soldier fly larvae (Hermetia illucens)
• Best for: Protein and calcium supplementation
• Key nutrition: ~40% protein, naturally very high in calcium
• Calcium to phosphorus: Positive ratio - rare among feeder insects
• Feed to: Isopods, millipedes, cockroaches, beetle larvae, springtails, and beyond the inverts, reptiles, turtles, fish and garden birds
• How often: As an occasional supplement, not a staple
• Storage: Cool, dry, and sealed - keeps for months
• Sizes: 50g, 100g, 250g

Why Calciworms For Invertebrates?

Most keepers reach for a protein food like fish flake or dried shrimp now and then, and rightly so - but the majority of feeder insects have an inverted calcium-to-phosphorus ratio, meaning they actually work against calcium levels rather than for them. Calciworms are the exception. They carry a positive calcium-to-phosphorus ratio, so they top up protein and calcium at the same time, which matters enormously for any invertebrate that has to rebuild a shell or exoskeleton every time it moults.

In my experience, a varied diet is the single biggest driver of breeding, and consistent breeding is the clearest sign that a colony has settled. Calciworms are one of the ingredients I rotate through to keep that variety up. They sit alongside the rest of our drygoods and accessories range rather than replacing leaf litter and rotting wood, which should always form the bulk of what your animals eat.

Feeding Different Animals

Isopods. This is where calciworms earn their place. Protein-hungry species like our best-selling Dairy Cow isopods (Porcellio laevis) have a high protein requirement, and an underfed Porcellio colony will start nibbling tankmates or each other - so a regular protein source is important, not just a nicety. The whole Porcellio genus benefits. For the calcium-hungry side of the hobby - Armadillidium morphs like Magic Potion with their thick, mineral-heavy shells, and Cubaris species such as the Panda King - calciworms double up as a protein treat and a calcium source in one.

Millipedes. A millipede's long, many-segmented exoskeleton is calcium-hungry, and calcium supports healthy moulting across the board. Crushed calciworms scattered on the substrate are readily taken by most of our millipedes.

Cockroaches and beetle larvae. Growing grubs and our cockroaches put protein to work quickly, and calciworms are an easy, mess-free way to deliver it.

Springtails. They won't tackle a whole larva, but springtails will happily graze on softened, rehydrated pieces alongside the microfauna already breaking them down.

Reptiles. Insect-eating lizards that will take food that isn't moving, bearded dragons among them, often eat calciworms as an extra alongside live insects, and the calcium is as welcome in a growing reptile as in a moulting isopod. A few minutes in warm water softens them and puts some moisture back.

Turtles, terrapins and fish. Aquatic turtles and terrapins take them as a treat, as do larger pond and aquarium fish such as koi. Keep them as an extra on top of a complete pellet rather than the main food.

Garden birds. Robins, blackbirds and tits will take them from a dish or bird table. Offer small amounts, soak them in spring and summer when adults may carry them to chicks, and clear anything left by dusk.

Not for chickens or hedgehogs. UK feed rules don't allow dried insects to be fed to farmed birds, and that includes backyard hens. Hedgehog rescues advise against calciworms as well as mealworms, so please leave them out of hedgehog feeding. Everything on our shelf that suits reptiles, turtles and fish is gathered in foods for reptiles, turtles and fish.

How To Feed Them

I feed calciworms in small amounts on the drier side of the enclosure, where they won't spoil as fast. For smaller species and mancae, crush or crumble them so the pieces are manageable; for larger Porcellio and millipedes you can offer them whole or lightly broken up. If you want them taken faster, a quick soak in a little water softens them and releases more scent, which tends to bring animals up out of the substrate.

The golden rule with any dried food is not to overdo it. Offer a little, let the colony work through it over a day or two, and remove anything left uneaten before it draws mould. As a supplement fed a couple of times a week alongside a good base of leaf litter and rotting wood, calciworms slot neatly into a varied diet without any risk of overfeeding.

Storage

Kept somewhere cool, dry, and sealed, dried calciworms last for months without any special handling - no refrigeration needed. Reseal the bag after each use to keep them dry and to preserve the scent that makes them appealing in the first place.

Our guide to feeding insects and protein to your isopods singles out black soldier fly larvae as naturally higher in calcium than other commonly available feeders.

Frequently Asked Questions

What are calciworms?

Calciworms are the dried larvae of the black soldier fly (Hermetia illucens). They're also sold as soldier fly larvae, black soldier fly larvae, BSFL, calcium worms, or soldier grubs - all the same thing.

Are calciworms good for isopods?

Yes. They're an excellent supplementary food for isopods, providing both the protein that species like Porcellio laevis need and the calcium that all isopods need for healthy moulting. Feed them as an occasional supplement rather than a staple, keeping leaf litter and rotting wood as the base of the diet.

Do calciworms have more calcium than mealworms?

Yes, considerably more - calciworms carry many times the calcium of mealworms, and unlike most feeder insects they have a positive calcium-to-phosphorus ratio. That's the main reason to choose them over mealworms as a supplement for moulting invertebrates. Our calciworms against mealworms comparison sets out the numbers and which animals each suits.

How often should I feed calciworms to invertebrates?

As a supplement rather than a staple - a small amount a couple of times a week works well for most colonies. Leaf litter and decaying wood should still make up the bulk of the diet.

Can I feed dried calciworms to millipedes?

Yes. Millipedes benefit from the calcium for their long exoskeleton and moulting. Crush or crumble the larvae and scatter them on the substrate.

Do calciworms need to be soaked before feeding?

Not necessarily - most invertebrates take them dry. Soaking softens them and releases more scent, which can help if you want them eaten faster or if you're feeding smaller species.

How do I store dried calciworms?

Keep them cool, dry, and sealed. They'll last for months with no refrigeration. Just reseal the bag after each use.

Can reptiles eat dried calciworms?

Yes, as an extra. Lizards that accept food that isn't moving, bearded dragons among them, often take them, and the positive calcium-to-phosphorus ratio suits growing animals. Soak them briefly first, and keep live insects as the main diet.

Can I feed dried calciworms to chickens?

No. In the UK, dried insects can't legally be fed to farmed birds, and that includes backyard hens.