Hornworms and silkworms are both soft-bodied caterpillars sold as treat or supplementary feeders, and they get talked about as though they were the same thing. They are not. One of them triples in size in a week and the other one needs feeding every day. This guide covers what each is, how fast each grows, what the toxicity question about hornworms actually says, how each keeps, and which one suits the way you feed.
What each one is
Hornworms are the larvae of Manduca sexta, the tobacco hornworm, a sphinx moth. In the trade they arrive as bright green caterpillars in a ventilated cup with a prepared diet already in it. The larva passes through five instars, and at 25 °C the average time spent in each is roughly 2.3, 2.0, 2.2, 3.1 and 8 days. Read that sequence again: almost all the growth happens at the end, quickly.
Silkworms are the larvae of Bombyx mori, domesticated for silk production over thousands of years. They are the most thoroughly domesticated insect in the trade. The adult moth cannot fly and the species cannot survive without people. Larvae feed on mulberry leaf or a mulberry-based chow, are reared at around 24 to 28 °C, and take roughly 24 to 28 days to go through the larval stage under good conditions.
We sell both hornworms and silkworms, and both are supplementary rather than staple.
Growth rate is the whole story
Hornworms grow fast enough that the size you ordered is a description of one particular week. A cup of small hornworms suits a juvenile animal for a few days and then does not. Keepers manage this by holding the cup cooler, which slows development, and by feeding them out on a schedule rather than treating a cup as stock.
Silkworms grow steadily over a much longer window, and the size you ordered stays roughly the size you ordered for long enough to plan around. That predictability is the main practical argument for silkworms, and it is rarely the one people lead with.
The consequence for ordering is simple. Buy hornworms in the quantity you will actually use inside a week or two, and check the animal's mouth width against the size rule on our dubia roach size chart for the size you will be feeding at the end of that period, not the size in the cup today.
Nutrition, in broad terms
Both are soft, high-moisture, low-fat feeders, which is what makes them useful as a break from beetle larvae. Hornworms are the wetter of the two by a clear margin, and are often used specifically as a water-carrying feeder for an animal that is not drinking well. Silkworms carry more substance per worm and are the better of the two if the goal is a meal rather than hydration.
Neither is a calcium source on its own, and both still need dusting for most captive insectivores. The bearded dragon feeder guide has a nutrition table, with sources, that includes both.
The hornworm toxicity question
This comes up every time hornworms are mentioned, and it is usually stated more confidently than the evidence supports.
Manduca sexta is a solanaceous feeder in the wild, on tobacco, tomato, pepper and eggplant. Larvae feeding on nicotine-containing plants handle the nicotine rather than being poisoned by it, and published work has shown that a small fraction of ingested nicotine, on the order of well under one percent, is moved into the hemolymph and exhaled through the spiracles, where it deters predatory spiders. So a hornworm off a tobacco plant is not a neutral object.
What follows from that for a keeper is narrow and practical: feed captive-bred hornworms reared on a prepared diet, and do not collect caterpillars off your tomato plants to feed to an animal. That is the same advice that applies to any wild-caught invertebrate, where pesticide exposure is also a concern. If an animal has already eaten a wild-collected caterpillar and is unwell, that is a call to an exotics vet, not a question for a shop page.
Keeping them once the box arrives
Both are more fragile in transit than beetle larvae, so open the box as soon as it arrives. The arrival guide covers the first hour and the heat pack guide explains why a cup of caterpillars is the hardest thing on the shipping list to get right in either direction.
| Hornworms (Manduca sexta) | Silkworms (Bombyx mori) | |
|---|---|---|
| Arrives as | Cup with prepared diet included | Larvae plus chow or mulberry, fed by you |
| Daily work | Near none until the cup is outgrown | Fresh food and cleaning, most days |
| Growth | Very fast; most of it in the final instar | Steady over roughly four weeks |
| Refrigeration | No. Cooler slows them; cold kills them | No |
| Main failure mode | Condensation and crowding in the cup; outgrowing the animal | Mold and disease in the food; a colony crashes together |
| Moisture content | Very high | High |
| Handling | Fragile; ruptures easily | Fragile; ruptures easily |
| Feeding response | Strong. Movement and color both help | Weaker. Slower and paler |
The guide to hornworm and silkworm care has the maintenance detail for both. Neither needs much in the way of equipment beyond what they ship in, which is unusual on this list.
Where the hornworm is the wrong choice
Hornworms are the more photogenic feeder, they get taken enthusiastically by bearded dragons and larger lizards, and any shop would be happy to sell them to you. Several cases point the other way.
- You want the feeder to be a meal. Hornworms are mostly water. An animal that eats a large hornworm has had a drink with some substance in it, not a substantial feed.
- You buy in advance. A cup you plan to use over a month is a cup that will be full of pre-pupal caterpillars long before you get there.
- Small animals. The usable window on a hornworm at the small end is short, because it does not stay small.
- Fussy eaters. Keepers commonly report animals refusing ordinary feeders after a run of hornworms. Treat this as a reason for moderation rather than a proven mechanism, but the pattern is reported often enough to plan around.
The mirror case for silkworms: they are the wrong choice if you do not want a daily job. A silkworm order is a small livestock commitment for as long as it lasts, and if you are away for a week you will come back to a problem.
Pick this one if…
- Pick hornworms if you want a hydrating feeder for an animal that is off water, or a high-interest item to restart a poor feeder.
- Pick hornworms if you want zero maintenance and will use the cup quickly.
- Pick silkworms if you want a soft-bodied feeder that is closer to a meal and holds its size while you plan around it.
- Pick silkworms if you keep animals that need soft prey after a shed, dental issue or mouth injury, on veterinary advice rather than your own.
- Pick neither as a staple. Both are supplementary. The bulk of a diet comes from somewhere else, which is what choosing a staple feeder insect is about.
Because both are fragile in transit, read our shipping and live arrival terms before ordering either. They also explain when we hold an order for heat, cold or storms.