Hornworms are one of the best feeder insects. They're hydrating, nutritious, and low in fat.
Hornworms' biggest "drawback" is that they grow and mature quickly! That's great if you're feeding a big critter that needs a ton of insect-based protein, like monitor lizards, tegus, and large chameleons. It's not great if you're feeding a small lizard, like a leopard gecko, or a lizard that doesn't eat tons of bugs, like a bearded dragon.
Luckily, we're here to add a few tricks to your sleeve if you're trying to make your hornworms grow slower. With some know-how, you might be able to stop them from pupating or getting too big for your pet before you can feed them off.
Low Ambient Temperatures
Hornworms are happiest and grow the fastest at temperatures around 81°F. Under these ideal conditions, hornworms complete their egg-to-adult cycle in 30 days or less. That's great if you need to get your worms as big as possible, as fast as possible.
To slow down that process, you can keep hornworms in a room as cold as 50°F. In doing so, you can make them last another week or two by extending their entire growth cycle from 30 days to as much as 48 days. They'll still grow and eat, just slower.
Refrigerator Cycling
If you're willing to take the risk that they might die, refrigerator cycling is something you might consider trying in a pinch. You can keep your hornworms in a wine cooler or the warmest area of your fridge (no colder than 45°F) for 48 hours, take them out to allow them to recover and eat for 24 hours, and put them back in the fridge for another 48 hours.
Again, they'll still grow and eventually pupate, but ideally, you can repeat this cycle indefinitely until that happens. There should be little to no growth during the 48 hours of chilling and average growth during the 24-hour warm-up.
There's always a risk that exposing your worms to the cold will kill them, even at temperatures above 45. Larger worms are more likely to survive the big chill - but that also means you have a smaller window of time until they pupate.
If you have a pet that doesn't require live insects, you can still feed dead, chilled hornworms at your discretion. Make sure that they don't look, smell, or feel gross. Otherwise, the cool temperatures should keep the worm's body fresh for a short time after it perishes, just like meat sold in human grocery stores.
Allow Them to Pupate
If you notice that your hornworms have begun to turn a reddish hue and wander around the cup, you have two options:
- feed them all off within the next 24-48 hours
- allow them to pupate, turn into moths, and feed the moths to your pet
Hornworms need to burrow into a substrate to pupate. Eco Earth, or coconut fiber, is a handy bedding material that most reptile keepers usually have on hand. It's also great for hornworm pupae! Put your restless worms in a ventilated container with a dish of moist coconut fiber 2-3" deep. They'll still seem restless at first, but they should begin to burrow into the material within a few days.
If your hornworms were exposed to at least 14 hours of light per day (you can use constant lighting if you prefer), they should be ready to emerge as moths in about 2 to 3 weeks. Hornworms that receive too little or no light exposure go into diapause, extending the pupae stage by months. You can remove the pupae from the soil 7 days after they burrow, but be gentle!
You can feed the moths to your pet as soon as they emerge or give them a branch to climb onto so they can expand their wings for a few hours. Once their wings are thoroughly dried and expanded, the moths can fly - making for an entertaining, enriching, and physically active hunting experience for your pet!