If you have ever wondered where do tomato hornworms go during the day, the answer is surprisingly simple: they vanish into the soil. Hornworms burrow into the top few inches of soil at dawn, emerging again only when evening temperatures cool. This daily disappearing act is a survival strategy that keeps them safe from birds and the harsh midday sun.
You might notice chewed leaves and dark droppings on your tomato plants, but the caterpillar itself is nowhere to be found. That is because they are hiding right beneath your feet, just a few inches down. Understanding this behavior is the key to controlling them in your garden.
Where Do Tomato Hornworms Go During The Day
During daylight hours, the hornworm is not lounging on the leaf surface. It is below the soil line, usually within the top 2 to 4 inches of loose dirt. They do not dig deep tunnels like moles. Instead, they wiggle down using their prolegs, creating a small cavity where they rest until dusk.
This behavior is triggered by light intensity. When the sun rises, the hornworm finishes its nightly feeding and drops to the ground. It then burrows horizontally or slightly downward, seeking moisture and darkness. The soil also provides a stable humidity level, which prevents the caterpillar from drying out.
Why They Hide In The Soil
There are three main reasons why this burrowing habit is so important for the hornworm’s survival:
- Predator avoidance: Birds, wasps, and predatory insects hunt by sight. A green caterpillar on a green leaf is easy to spot, but a caterpillar hidden in dirt is invisible.
- Temperature regulation: The soil stays cooler than the air during the afternoon. This prevents the hornworm from overheating.
- Moisture retention: The topsoil retains moisture from the night, keeping the hornworm hydrated until it emerges again.
Interestingly, the hornworm does not just pick any spot to hide. It tends to burrow near the base of the host plant, usually within a 6-inch radius of the stem. This short distance allows it to climb back up quickly when the sun goes down.
The Daily Cycle Of A Hornworm
To truly understand where they go, you need to map out their 24-hour routine. Here is a typical schedule for a tomato hornworm during the summer months:
- Dusk (7:00 PM – 9:00 PM): The hornworm emerges from the soil and climbs the nearest stem.
- Night (9:00 PM – 2:00 AM): It feeds heavily on leaves and green fruit, consuming large amounts of foliage.
- Pre-dawn (3:00 AM – 5:00 AM): Feeding slows down, and the hornworm begins to descend the plant.
- Dawn (5:00 AM – 6:00 AM): It reaches the soil surface and burrows headfirst into the ground.
- Day (6:00 AM – 7:00 PM): It remains motionless underground, digesting its food and hiding from predators.
This cycle repeats every day for about 4 to 6 weeks, until the hornworm is ready to pupate. When it reaches full size, it burrows deeper (around 4 to 6 inches) and forms a brown pupal case. It will stay in that soil through the winter, emerging as a moth the following spring.
How To Find Them During The Day
Now that you know they are in the soil, you might be tempted to dig them up. However, digging randomly is not efficient. Instead, you can use a simple flashlight trick to locate them at night, or you can check for their daytime signs.
Look For The Droppings
Hornworm frass (droppings) is a dead giveaway. These are dark green or black pellets, about the size of a small peppercorn. They accumulate on the lower leaves and on the soil surface directly under the feeding site. If you see these pellets, you know a hornworm is hiding nearby.
To find the actual caterpillar during the day, follow these steps:
- Look for fresh droppings on the ground under the plant.
- Gently brush aside the top layer of soil (1-2 inches) around the base of the stem.
- Look for a curled, green or brown caterpillar resting in a small cavity.
- If you do not find it immediately, check the soil in a 6-inch radius around the stem.
Another trick is to water the soil lightly. Hornworms sometimes react to the moisture by wiggling, which makes them easier to spot. But be careful not to drown them, as you want to remove them, not just relocate them.
Using A Flashlight At Night
The most effective way to catch hornworms is to go out after dark with a UV flashlight. Hornworms glow under ultraviolet light because of a protein in their bodies. This makes them stand out like neon signs against the green leaves.
Here is how to do it:
- Wait until at least 30 minutes after sunset.
- Shine the UV light directly on the tomato foliage.
- Scan the undersides of leaves and the stems.
- Pick off any glowing caterpillars and drop them into soapy water.
This method is much faster than digging. You can cover a whole row of tomatoes in 10 minutes, whereas digging takes much longer and disturbs the roots.
Why You Should Remove Them
You might be wondering if it is worth the effort to hunt for these hidden pests. The answer is yes, because a single hornworm can defoliate an entire plant in a week. They eat voraciously, and their large size means they consume more than smaller caterpillars.
If you leave them alone, they will not just eat the leaves. They also bore into the green tomatoes, leaving large, open wounds. These wounds invite rot and disease, ruining your harvest. By removing them during the day, you stop the damage before it starts.
Natural Predators That Help
Before you go on a hunting spree, check the hornworm for small white cocoons on its back. These are the pupae of a parasitic wasp called Cotesia congregata. If you see these, do not kill the hornworm. Instead, leave it alone, as the wasps will hatch and kill the hornworm naturally.
These wasps are beneficial to your garden. They will also parasitize other pests, so it is wise to let them complete their life cycle. You can also encourage these wasps by planting dill, fennel, and yarrow near your tomatoes.
Preventing Them From Burrowing
If you are tired of dealing with hornworms, you can take steps to prevent them from burrowing in the first place. One effective method is to till the soil lightly in the fall and spring. This exposes the pupae to cold weather and birds, killing them before they can emerge.
Another option is to use a barrier. You can place a cardboard collar around the base of the tomato stem, extending it 2 inches into the soil. This physically blocks the hornworm from burrowing near the plant, forcing it to hide elsewhere where you can find it easily.
Using Row Covers
Row covers are another great option. These are lightweight fabrics that you drape over your plants. They prevent the adult moths from laying eggs on the leaves in the first place. Without eggs, there are no hornworms.
However, you must remove the row covers when the tomatoes start flowering. The plants need pollinators to set fruit. You can put the covers back on after the flowers are pollinated, but this is extra work. Many gardeners find that simply hunting at night is easier.
Frequently Asked Questions
Q: Do tomato hornworms stay in the soil all day?
A: Yes, they stay underground from dawn until dusk. They only come up to feed at night when the temperature drops.
Q: How deep do hornworms burrow?
A: Most hornworms stay within the top 2 to 4 inches of soil. They go deeper, around 4 to 6 inches, only when they are ready to pupate.
Q: Can I find hornworms by digging up the soil?
A: You can, but it is time-consuming. It is easier to look for their droppings on the ground or use a UV flashlight at night.
Q: What time of night do hornworms come out?
A: They usually emerge about 30 minutes after sunset. They are most active between 9 PM and 2 AM.
Q: Will hornworms kill my tomato plant?
A: A single hornworm can strip a small plant of all its leaves in a few days. This can kill young plants, but mature plants usually survive, albeit with reduced yield.
So the next time you see chewed leaves but no caterpillar, remeber that it is hiding right under the soil. Grab a flashlight, wait for dark, and you will catch it in the act. The key is to be patient and check your plants every few days during the summer months.
You can also try companion planting. Marigolds and basil are said to repel the adult moths. While this is not a guaranteed solution, it adds color to your garden and may reduce the number of eggs laid. Combine this with nightly checks, and you will keep your tomatoes safe all season long.
Finaly, do not forget to clean up fallen leaves and debris at the end of the season. This removes potential hiding spots for pupae. A clean garden is a healthy garden, and it will save you a lot of trouble next year.
Now you know the answer to the question. They are not gone, they are just waiting for the sun to set. So go out there, check your plants, and win the battle against these hungry caterpillars.