If you've browsed bird food recently, you've probably noticed that mealworms are no longer the only larvae on the shelf. Calci worms — sometimes listed as calciworms or black soldier fly larvae — have become increasingly popular, and the question we get asked more than almost any other is: which one should I be buying?
The honest answer is that they complement each other rather than compete. But understanding what each one actually does will help you make smarter choices for the birds in your garden — especially if you're trying to support them through specific times of year like breeding season, winter, or fledging.
What Are Mealworms?
Mealworms are the larvae of the darkling beetle (Tenebrio molitor). They're the golden-brown, slightly crunchy larvae you'll recognise from most bird food aisles — and birds absolutely love them.
They're particularly rich in protein and fat, which makes them one of the most energy-dense foods you can offer. That high-protein profile is what makes them so valuable for insect-eating birds, especially during spring and summer when parent birds are working flat out to feed their chicks.
Birds that tend to go absolutely mad for mealworms:
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Robins — mealworms are probably their number one food
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Blackbirds and thrushes — ground feeders that will clear a dish in minutes
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Blue tits and great tits — particularly during breeding season
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Wrens — hard to spot, but very partial to a mealworm
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Starlings — they will demolish whatever you put out, frankly
Dried mealworms are the most practical choice for most garden feeders. They store well, last a long time, and can be scattered on a bird table, ground feeder or flat dish. During dry weather or breeding season, soaking them briefly in warm water is worth doing — it softens them and adds a bit of moisture, which is particularly helpful for fledglings still learning to eat.
What Are Calci Worms?
Calci worms are the larvae of the black soldier fly (Hermetia illucens). They look similar to mealworms but are a bit smaller, softer, and — as the name suggests — significantly higher in calcium.
That calcium content is the main differentiator. Calci worms contain dramatically more calcium than mealworms, which makes them especially valuable for:
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Breeding birds — females need significant calcium to produce strong eggshells
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Fledglings — developing bones need calcium in the early weeks
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Smaller, softer-billed birds that struggle with harder foods
Because calci worms are softer and smaller, they're also easier for young birds to handle and swallow. If you've got nesting birds in or near your garden — or you can hear the sound of hungry chicks — calci worms are a brilliant thing to have on your feeder.
The Key Differences at a Glance
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Protein: mealworms win — higher protein content per gram
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Calcium: calci worms win — significantly more than mealworms
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Texture: calci worms are softer and smaller, easier for young birds
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Fat content: mealworms are higher in fat, great for cold-weather energy
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Year-round value: both, but calci worms shine most in breeding season
So Which Should You Buy?
Both, ideally — and that's not just us trying to sell more product. Mixing dried mealworms and calci worms in the same feeder gives visiting birds access to both high-quality protein and the calcium they need. It's a more balanced offering than either alone.
If you can only choose one, think about what you're trying to support. Feeding mainly through winter when birds need dense calories? Lean towards mealworms. Heading into spring with nesting birds nearby? Calci worms are the priority. Notice a lot of fledglings visiting the garden? Calci worms again.
One thing worth knowing: neither mealworms nor calci worms should be the only food on your feeders. They're brilliant supplements, but birds also need seeds, fat-based foods, and ideally fresh water every day. Think of them as the protein course in a balanced garden bird menu.
A Note on Hedgehogs
If you've got hedgehogs visiting your garden — lucky you — be aware that mealworms are not good for them in quantity. The high phosphorus content in mealworms can disrupt calcium absorption in hedgehogs and lead to serious health issues. Calci worms are a much better choice if you're trying to support both your birds and any visiting hedgehogs.
Walter Products' dried mealworms and calci worms are available individually or together — and our spend threshold for a free tub of mealworms means it's often worth picking up both at the same time. Find them in our bird food range at walterproducts.co.uk.
