Silkworms 101: The Complete Guide for Reptile Keepers

Silkworms are one of the strangest organisms in the reptile-keeping hobby. They cannot survive in the wild. They eat only mulberry leaves. They've been domesticated for over 5,000 years, originally for textile production. Modern reptile keepers prize them for an entirely different reason: they're one of the most nutritionally complete feeder insects available, with a calcium-to-phosphorus ratio that almost no other commercial feeder can match. This is the complete guide — what they are, why they matter, how to feed them, and how to use them across the reptiles you actually keep.

What silkworms are

Silkworms (Bombyx mori) are the larvae of the silk moth. They go through five instar stages over a 28-day period, growing from 3 mm hatchlings to 7 cm pre-pupation larvae before spinning silk cocoons. The species has been selectively bred since approximately 3000 BCE for silk production, and that domestication has fundamentally changed the organism — adult moths cannot fly, are largely blind, and rely on humans for everything from feeding to reproduction. They are the only domesticated insect species in commercial use.

For reptile keepers, the relevant biology is simpler. Silkworms eat mulberry leaves (or commercial mulberry chow, which is dried mulberry powder rehydrated with water). They concentrate the nutrients in those leaves into a soft-bodied, low-fat, calcium-rich feeder that's safe for hatchlings, easy on adults, and exceptionally well-suited to reptiles prone to obesity or metabolic bone disease.

Why silkworms matter nutritionally

The calcium-to-phosphorus ratio

The single biggest reason experienced keepers value silkworms is their calcium balance. Most commercial feeder insects have a Ca:P ratio between 1:8 and 1:20 — far short of the 2:1 a growing reptile needs. Keepers compensate with calcium dusting, but dusting only goes so far.

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 (BSFL)	3 : 1

Silkworms and BSFL are the only two commonly bred feeders that get close to natural calcium balance.

Low fat

At ~10% fat by dry weight, silkworms are dramatically leaner than most alternatives — half what mealworms deliver, a fifth of waxworms. For adult reptiles that gain weight easily on rich diets, silkworms let you offer real meal volume without the fat load.

Complete amino acid profile

Silkworm protein contains all nine essential amino acids in ratios that suit vertebrate metabolism. Studies in aquaculture have shown silkworm meal can replace 30–50% of fishmeal in growth diets without performance loss — a strong indicator of nutritional completeness.

Antimicrobial peptides

Silkworms produce a class of immune compounds called cecropins that resist bacterial colonization. The practical effect for keepers: silkworms are unusually clean to feed — they rarely transmit pathogens to the animals consuming them.

How to feed silkworms (basic care)

Temperature

Silkworms thrive at 72–82°F (22–28°C). Below 70°F they grow slowly; below 60°F they die. Never refrigerate silkworms — cold is the most common cause of mass die-offs.

Feeding

Silkworms eat only mulberry. Most keepers use commercial mulberry chow (dried mulberry powder rehydrated with hot water, set into a paste). Refresh chow every 2–3 days. If you have a clean mulberry tree on hand, fresh leaves work even better.

Storage container

The shipping container is fine for the first batch. For longer-term keeping, a shallow plastic bin with a vented lid works. Silkworms don't climb well, so deep walls aren't needed.

Cleaning

Spot-clean every other day — silkworm waste (frass) builds up fast. Replace chow on a 2–3 day cycle. Watch for mold; mold is a silkworm killer.

For deeper detail on raising silkworms, including the full lifecycle and breeding considerations, see our complete silkworm care guide.

The 28-day lifecycle

Silkworms grow on a strict schedule:

• Days 0–3: hatchlings, 3 mm
• Days 4–10: first and second instars, 5–15 mm
• Days 11–18: third and fourth instars, 15–35 mm — peak feeding-size for most reptiles
• Days 19–25: fifth instar, 35–70 mm
• Days 26–28: pre-pupation, silkworms stop eating and spin cocoons

You can't pause silkworms — once they hatch they're on the clock. Match your order quantities to your weekly feed-off rate.

Sizing silkworms to your reptile

The non-negotiable rule for any insectivorous reptile: prey should be no wider than the space between the animal's eyes. Oversized prey causes impaction. Silkworm sizing by reptile size:

• Hatchlings (under 4 in): very small silkworms, 1–1.5 cm
• Juveniles (4–8 in): small silkworms, 2–3 cm
• Sub-adults (8–14 in): medium silkworms, 3–4 cm
• Adults (14+ in): medium-large silkworms, 4–6 cm

Where silkworms fit in the diet

Silkworms are a supplement, not a staple. Treat them as 20–30% of insect intake for most insectivorous reptiles:

• Hatchling and juvenile insectivores: silkworms 2–3× per week, alongside crickets and roach staples.
• Adult reptiles: silkworms 1–2× per week, more if managing weight on the leaner side.
• Animals with kidney concerns or MBD risk: silkworms can be a near-staple, with crickets used to trigger feeding response.

Variety beats any single feeder. A 100% silkworm diet leaves the gut underexposed to chitin (which has a healthy role in moderation) and runs into cost ceilings quickly.

Species-specific guides

For depth on individual species, we have dedicated guides:

• Silkworms for bearded dragons — calcium balance and obesity management
• Silkworms for chameleons — kidney protection and hydration
• Silkworms for leopard geckos — lean feeder for fat-tail health
• Silkworms for baby bearded dragons — sizing rules for hatchlings
• Silkworms for anoles, tegus, tree frogs, and others

Common keeper mistakes

• Refrigerating silkworms: cold kills them. Room temperature is correct.
• Single-feeder diet: variety matters more than any one feeder's quality.
• Oversizing: impaction is irreversible. The eye-spacing rule exists for a reason.
• Letting chow mold: silkworms die fast in moldy conditions. Refresh every 2–3 days.
• Ordering too many: silkworms can't be paused. Match batch size to weekly feed-off rate.

Comparisons with other feeders

For depth on how silkworms compare to other common feeders:

• Silkworms vs crickets — the staple-vs-supplement question
• Silkworms vs hornworms — both soft-bodied, very different roles

Bottom line

Silkworms are one of the most nutritionally valuable feeders available — best-in-class calcium ratio, low fat, easy digestion, complete amino acid profile. They cost more per gram than crickets or roaches, and they can't be the entire diet. But used as 20–30% of insect intake, they meaningfully improve long-term reptile health in ways that supplementation alone cannot. Browse our silkworm collection or the rest of our Creature Insights blog.