Silkworms vs BSFL: Two Specialists, One Rotation
These are the two feeders I get asked to pick between most, and the question itself is a little off. Silkworms and black soldier fly larvae aren't competitors — they're specialists that happen to sit at the same "premium feeder" price point. Silkworms dominate one column of the nutrition chart, BSFL dominate a completely different one. Once you see that, the answer stops being "which" and becomes "both, for different reasons."
Head to head
| Category | Silkworms | BSFL |
|---|---|---|
| Primary strength | Lowest fat (~1%) | Highest calcium (~9,340 mg/kg) |
| Fat | ~1% | ~14% |
| Calcium | ~340 mg/kg | ~9,340 mg/kg (about 27x more) |
| Ca:P ratio | ~0.77:1 | ~6.92:1 |
| Moisture | ~83% | ~61% |
| Chitin | None | Low-moderate |
| Calcium dusting needed? | Yes | No |
| Storage | Room temp, fresh chow, ~1-2 weeks | Fridge, no feeding, ~2-3 weeks |
That table tells the whole story. Silkworms are the leanest, softest, most hydrating feeder you can buy. BSFL are a calcium powerhouse you never have to dust. Neither does the other's job well.
Choose silkworms when
- Fat is the concern. For obesity-prone animals — leopard geckos with fattening tails, sedentary adult bearded dragons, chameleons — ~1% fat is the safest supplement going.
- You need the softest possible feeder. Zero chitin makes silkworms ideal for hatchlings, recovering animals, and sensitive digestive systems.
- Hydration matters. At ~83% moisture, they put water into a gecko that won't drink from a dish.
- You're fighting a picky eater. Their pale color and slow wriggle trigger feeding responses in animals refusing other food.
Note one thing the table makes clear: silkworms' ~0.77:1 calcium ratio is still below 1, meaning they're mildly phosphorus-heavy like most feeders. So you do still dust them with calcium. They win on fat and softness, not on minerals.
Choose BSFL when
- Calcium is the priority. Growing juveniles, egg-laying females, and any animal you're protecting from metabolic bone disease benefit from BSFL's natural surplus.
- You want a feeder that needs no dusting. This is the one feeder where you can skip the powder entirely.
- You want easy storage. Fridge them and forget them for a couple of weeks.
The real answer: use both
In my rotation they're complementary slots, not an either/or:
- Daily: discoid roaches — the protein staple.
- 2-3x/week: silkworms — low fat, hydration, soft body.
- 2-3x/week: BSFL — calcium, no dusting.
- 1-2x/week: hornworms — hydration and appetite.
If I had to point a new keeper at one to start with, I'd ask what their animal needs more — leanness or calcium — and buy that first. For most well-fed adult geckos that's leanness, so I'd reach for low-fat silkworms and add BSFL the following week. But the honest goal is to have both in the fridge and the bin, because together they cover the two gaps a roach staple leaves open.
See exactly how these slot into a leo's week in my complete leopard gecko diet guide, and compare silkworms to the fattier options in silkworms vs superworms.
Sources: Finke, M.D. (2013). "Complete nutrient content of four species of feeder insects." Zoo Biology 32:27-36. doi:10.1002/zoo.21012 · University of Florida IFAS Extension — Black Soldier Fly