Silkworms 101: The Complete Guide for Reptile Keepers
- Role
- Rotation supplement
- Protein
- ~11%
- Fat
- ~2%
- Moisture
- ~80%
- Chitin
- very low
- Ca:P
- ~1:2
- Calcium-rich
- No (dust it)
- Best for
- Soft-bodied protein for picky or recovering animals
Silkworms are one of the strangest organisms in this hobby. They can't survive in the wild, they eat only mulberry, and they've been domesticated for over 5,000 years, originally for silk. Reptile keepers prize them for a completely different reason: pound for pound, they're one of the most nutritionally complete feeders you can buy, with a calcium-to-phosphorus ratio almost nothing else matches. This is the full picture, what they are, why they matter, and how to use them.
What silkworms are
Silkworms (Bombyx mori) are the larvae of the silk moth. They move through five instar stages over about 28 days, growing from 3 mm hatchlings to 7 cm pre-pupation larvae before spinning cocoons. Millennia of selective breeding have changed the animal fundamentally: adult moths can't fly, are nearly blind, and depend on humans for everything. It's the only fully domesticated insect in commercial use.
For us, the biology that matters is simpler. Silkworms eat mulberry (leaves or rehydrated mulberry chow) and concentrate those nutrients into a soft, low-fat, calcium-rich feeder that's safe for hatchlings and easy on animals prone to obesity or metabolic bone disease.
Why silkworms matter nutritionally
The calcium-to-phosphorus ratio
This is the headline. A growing reptile needs roughly 2:1 calcium to phosphorus, and most feeders fall catastrophically short.
| Feeder | Ca:P (approx) |
|---|---|
| Crickets | 1:9 |
| Mealworms | 1:14 |
| Superworms | 1:18 |
| Discoid roaches | 1:3 |
| Silkworms | 1:1.4 |
| Black soldier fly larvae | 3:1 |
Silkworms and BSFL are the only commonly bred feeders that get close to natural calcium balance. With most feeders you compensate by dusting, but dusting only goes so far. The Merck Veterinary Manual details why chronic calcium-phosphorus imbalance drives metabolic bone disease.
Low fat
At roughly 10% fat by dry weight, silkworms are dramatically leaner than most alternatives, about half what mealworms carry. For animals that gain weight easily, that lets you offer real meal volume without the fat load.
Complete amino acid profile
Silkworm protein contains all nine essential amino acids in vertebrate-friendly ratios. Aquaculture studies have shown silkworm meal can replace 30-50% of fishmeal in growth diets without performance loss, a strong signal of nutritional completeness.
Antimicrobial peptides
Silkworms produce immune compounds called cecropins that resist bacterial colonization. The practical payoff: silkworms are unusually clean to feed and rarely transmit pathogens.
How to feed silkworms (basic care)
Temperature: 72-82°F. Below 70°F they slow; below 60°F they die. Never refrigerate them. Cold is the most common cause of mass die-offs.
Feeding: Mulberry only. Most keepers use mulberry chow (dried mulberry powder set with hot water into a firm paste). Refresh every 2-3 days. Fresh, pesticide-free mulberry leaves work even better.
Container: The shipping cup is fine for the first batch. For longer keeping, a shallow vented bin works. Silkworms don't climb well, so deep walls aren't needed.
Cleaning: Spot-clean every other day. Frass builds up fast, and mold is a silkworm killer.
The 28-day lifecycle
Silkworms run on a fixed schedule, and you can't pause it:
- Days 0-3: hatchlings, 3 mm
- Days 4-10: first/second instar, 5-15 mm
- Days 11-18: third/fourth instar, 15-35 mm, the peak feeding range for most reptiles
- Days 19-25: fifth instar, 35-70 mm
- Days 26-28: pre-pupation, they stop eating and spin
Match your order size to your weekly feed-off rate so you're not stuck with worms outgrowing your animal.
Sizing silkworms to your reptile
The non-negotiable rule for any insectivore: prey should be no wider than the space between the animal's eyes. Oversized prey causes impaction.
- Hatchlings (under 4 in): 1-1.5 cm
- Juveniles (4-8 in): 2-3 cm
- Sub-adults (8-14 in): 3-4 cm
- Adults (14+ in): 4-6 cm
Where silkworms fit in the diet
Silkworms are a supplement, not a staple, around 20-30% of insect intake for most insectivores. Hatchlings: 2-3x/week alongside roach or cricket staples. Adults: 1-2x/week, more if you're managing weight. Animals with MBD risk or kidney concerns can run them closer to staple level. Variety still beats any single feeder.
Common keeper mistakes
- Refrigerating them (cold kills, room temp is correct)
- Single-feeder diets (variety matters more than any one feeder)
- Oversizing (impaction is irreversible)
- Letting chow mold (refresh every 2-3 days)
- Ordering too many (they can't be paused)
Bottom line
Silkworms are among the most nutritionally valuable feeders available: best-in-class calcium ratio, low fat, easy digestion, complete amino acids. They cost more per gram than roaches and can't be the whole diet, but at 20-30% of intake they improve long-term health in ways supplementation alone can't. Browse silkworms at All Angles Creatures to start a batch.
Next reads: raising silkworms at home and silkworms for chameleons.