10 Things Worth Knowing About Silkworms (Biology, History, and Feeding)

I started keeping silkworms because they're one of the gentlest, most digestible feeders you can offer a reptile or amphibian — and they turned out to be one of the most genuinely interesting insects in the hobby. Bombyx mori has been bred by humans for over 5,000 years, and that long domestication shows up in everything from their biology to how you feed them. Here are ten facts worth knowing, with the keeper's angle on each.

1. They're caterpillars, not worms

Despite the name, silkworms aren't worms — they're the larval (caterpillar) stage of the silk moth, in the family Bombycidae. Like all moths they go through complete metamorphosis: egg, larva, pupa, adult. The "worm" you feed is the larva, and it's the only stage that eats.

2. The lifecycle is fast and four-staged

The whole cycle runs about six to eight weeks:

For a keeper, the larval stage is the whole game — that's your feeder window, so timing batches matters.

3. They've been fully domesticated for millennia

Silkworms were first domesticated in ancient China — sericulture dates back to at least ~2700 BCE — and they've been bred for silk so long that they're now entirely dependent on humans. They don't exist in the wild. That domestication is why they're so docile and easy to handle.

4. The adults can't fly

Selective breeding for silk stripped Bombyx mori of flight. The adult moths can't fly, live only about five days, and focus entirely on reproduction. Practically, that means an adult that emerges in your setup isn't going anywhere.

5. They eat one thing: mulberry

Silkworms feed almost exclusively on mulberry leaves (Morus species). Their digestive system — strong mandibles, a simple efficient gut — is specialized for it, and silk quality and growth both track leaf quality. Mulberry leaves bring protein for silk production plus vitamins (A, B1, B2, C) and minerals like calcium, magnesium, and iron. In practice most keepers raise silkworms on a prepared mulberry-based chow rather than fresh leaves year-round; just don't expect them to thrive on random greens.

6. They're a soft, digestible, calcium-friendly feeder

This is the part that matters most if you're feeding reptiles. Silkworms are low in fat, high in moisture, soft-bodied, and easy to digest — and they're relatively calcium-rich for an insect. That makes them one of the better staple-rotation or recovery feeders, gentler than fatty superworms or chitin-heavy mealworms. They still benefit from gut-loading and, for high-demand animals like growing or gravid reptiles, a light calcium dusting. (Black soldier fly larvae are the other feeder famous for a genuinely favorable calcium-to-phosphorus ratio; most feeders need supplementation.)

7. The silk is one continuous thread

Each silkworm spins its cocoon from a single continuous filament that can run roughly 1,000 to 3,000 feet long, extruded through a spinneret near its mouth in a figure-eight motion. The fiber is two proteins — fibroin (the strong core) and sericin (the sticky binder) — that harden on contact with air.

8. Their anatomy is built for the job

The larva's body is divided into head, thorax, and abdomen across 13 segments, with three pairs of true legs on the thorax and five pairs of prolegs on the abdomen for grip. They breathe through a tracheal system — small openings called spiracles along the body diffuse oxygen directly into the tissues, which supports their explosive larval growth.

9. Their history shaped global trade

Silk was a guarded Chinese state secret for centuries — at points, smuggling silkworms out was punishable by death. The Silk Road is literally named for the trade it carried, and sericulture eventually spread to India, Japan, the Byzantine Empire (via smuggled eggs around the 6th century CE), and later European hubs like Lyon and Venice. Silkworms quietly helped wire together the ancient economy.

10. They're a modern science workhorse

Beyond textiles, silkworms are a serious research organism. Their well-mapped genome makes them useful in genetics and as bioreactors for producing therapeutic proteins, and silk fibroin is studied as a biomaterial for sutures, tissue-engineering scaffolds, and drug delivery thanks to its biocompatibility and biodegradability. For a backyard feeder insect, that's a remarkable second career.

If you want to try silkworms as a feeder, All Angles Creatures' silkworm collection is where I source mine. On the nutrition logic — why most feeders need calcium and silkworms are a gentler exception — the Merck Veterinary Manual on reptile nutrition is a solid reference.

For other feeders to rotate alongside silkworms, see my guides to buying discoid roaches and buying superworms in bulk.