Dealing with hornworms in tomatoes isn’t always a straightforward decision. There are reasons some people choose to move them and not kill them.
Why?
That’s what we’ll talk about.
Along with how and where they should go.
Jump to:
- Save Your Tomatoes & Pollinating Hawk Moths
- Balance is Important in your Garden Too
- Some Real Reasons Not to Kill Horn Worms
- Pollination
- Supporting the parasitic braconid wasp population
- 7 Ways to Live with Hawk Moths and Hornworms
- 1. Plant Extra Tomatoes
- 2. Use a Floating Row Cover to Protect Your Tomatoes
- 3. Leave Them Be and Accept the Plant Damage
- 4. Move Hornworms to Host Weeds
- 5. Designate a Sacrificial Tomato Plant
- 6. Move Hornworms to a Different Host Garden Plant
- 7. Till Tomato Patches Before Winter
- We Can Live with these Weird Worms and Have Our Gardens, Too
Save Your Tomatoes & Pollinating Hawk Moths
The reason you might want to protect hornworms is that as adults, they become hawkmoths (the five-spotted hawkmoth and the Carolina Sphinx moth in the case of the caterpillars that live on tomato plants).
Here’s the thing about hawk moths: their larval stage is the tomato hornworm (or the tobacco hornworm in the case of the related tobacco hornworm, a close cousin that also frequents tomato plants).
But their adult stage is one of the hawkmoth species (well, two of them when we’re including the tobacco hornworm, and in their effects on the garden, they are about the same – there are many other species of hawk or sphinx moths).
In both the larval and the adult stage, there is an argument to be made against killing hornworms outright.
Balance is Important in your Garden Too
On the other hand, hornworms are very destructive.
- They can nearly entirely defoliate tomato plants and some other garden plants, too.
- Hornworms can completely kill some plants, especially smaller tomato varieties and small plants like peppers and eggplants.
- They may attack potatoes, too, because their host is plants in the nightshade family (solanaceous plants).
- Hornworms will even take large bites out of the fruits of these plants, causing rot, scarring, and sometimes eating entire fruits/vegetables (especially while they’re still small).
- Hornworms may completely eat flower buds (future tomatoes or veggies).
- When they strip leaves from sections of plants (or whole plants), this can result in sun scald on your tomatoes.
All of this can do a lot of damage – or nearly completely ruin – your tomato crop.
So, there has to be a balance.
Some Real Reasons Not to Kill Horn Worms
Most people err on the side of complete removal or killing of all hornworms they find in their tomato patch (or elsewhere on valuable plants in the garden). We pass no judgment, and this is surely an individual decision to be made.
Many different factors come into play.
Some of the reasons why people opt to protect hornworms are as follows:
Pollination
While hornworms are destructive pests, their adult stage, hawkmoths, are not.
Adult hawkmoths feed on nectar. They are active at night, as most moths are. You may not even see the adults that often.
Hawkmoths hover and feed on flowers with deep, trumpet-like shapes. They’re similar to hummingbirds that way. Jimsonweed, trumpet vine, and other bell-shaped flowers can be pollinated by hawkmoths.
One of the benefits of hawkmoths (aka sphinx moths) is that, because they feed at night, they are beneficial pollinators for plants whose flowers only open at night – moonflowers, for example.
As adults, the only harm hawk moths do to gardens is to lay more eggs that become destructive, nightshade foliage-feeding caterpillars.
That’s not nothing, but it’s worth knowing that once the caterpillars are adult moths, the damage is done.
That said, it should also be pointed out that hawkmoths and hornworms usually have two generations per season, so you could have more caterpillars upcoming.
The pupae also overwinter in cocoons in the soil and then hatch as egg-laying adults in the spring.
Which is to say, you’re not really done with hornworms after the first obvious caterpillars have their fill. There is future garden damage to consider, too, as well as increasing the population and growing it into an even larger problem.
Supporting the parasitic braconid wasp population
Have you ever seen hornworms with rows of white egg-like protrusions popping out of the skin on their backs?
These are the eggs of the parasitic wasp, the braconid wasp.
When you find hornworms sporting these, you should never kill them (even if you want those hornworms GONE!). You have better, more natural control of hornworms if you let these wasps complete their lifecycle and live to parasitize more worms.
This helps to keep a more natural level of balance and limits plant and fruit damage.
The other part of this is this: if you kill all the hornworms, you kill all the potential parasitic braconid wasps, too. We inadvertently collapse a very beneficial insect population. It’s not just tomato hornworms that the wasps help control, either.
These wasps are one of the primary natural controls (parasitoids) of dozens of types of damaging garden caterpillars, including cabbage loopers, army worms, and tent caterpillars (to name only a very few).
The University of Maryland says that as a group, parasitoid wasps, of which braconids are a member, “may be the single most important biological control method gardeners have.”
Hornworm eggs are food for other beneficial insects, too, including ladybugs, lady beetles, and lacewings.
We can see, then, how killing hornworms and removing an important host for the parasitic but beneficial braconid wasp might be something we should think twice about.
7 Ways to Live with Hawk Moths and Hornworms
The dilemma is this:
How can we live with the highly destructive tomato and tobacco hornworm, which eats four times its body weight in plant matter per day and still have a successful, food-yielding garden?
Here are seven things you can do:
1. Plant Extra Tomatoes
You don’t have to go overboard with overplanting. In other words, an extra plant or two will do the job and give you some options to work with. But it does help to have some spares and some plants to share if you don't want to kill the hornworms.
Obviously, this is a step that relies on some pre-planning. If you’re in the middle of your gardening season, it won’t do you much good this year, but it’s something you can plan for in the future.
The same goes for eggplant and peppers, though you will typically have more problems with hornworms on your tomatoes.
2. Use a Floating Row Cover to Protect Your Tomatoes
A floating row cover placed over tomato plants stops the hawk moths from laying their eggs (read: future caterpillars) on your tomato plants.
This will in no way kill the hornworms. The parents will lay their eggs elsewhere. Hopefully, that will be on some far-off relative of a nightshade weed that you don’t have to care about being defoliated by the hornworm.
Hornworms can’t exactly travel very fast or very far. They basically just eat the plant their eggs are laid on, or plants that are close enough to crawl to.
The idea here is that you control where hornworms live, but not that they live.
This can be a fine and easy balance to strike in your tomato garden.
Cover other host garden plants, too
Keep in mind that tomatoes are the favorite, but not the only, host plant that we value.
You’ll want to cover other potential host plants, too, especially since you are denying the moths their first choice (tomatoes).
If you only cover your tomato plants, instead of infesting your tomatoes, the moths will just move on to other host plants that you planted and lay their eggs there.
Those other plants are all small plants that are impacted more when hornworms find them.
Other plants to cover are tobacco, peppers, eggplant, and potatoes (probably in that order of worm preference).
3. Leave Them Be and Accept the Plant Damage
This can be hard to do. You work hard for your garden, and watching caterpillars the size of your finger chew it away is tough.
However, if you are not too overrun with hornworms, and the damage is limited enough to still give you all the tomato harvest you need, then ignoring them is an option that protects their pollinating and beneficial insect potential while still giving you what you need from the deal.
This is also where having an extra couple of plants comes in handy. Plant more than you think you need, so you think you can let the hornworms have some (within reason).
4. Move Hornworms to Host Weeds
This one could be a real win-win situation.
There are several weeds that are in the nightshade family. Solanaceous weeds like jimsonweed, horsenettle, and varieties of nightshade.
If you have these weeds in your yard, you can relocate hornworms to them. Let them finish off their lifecycle as they finish off the weeds.
That said, this is also a reason to keep your tomato rows weed-free, especially free of solanaceous weeds. They will be another draw and attraction for the moths to lay their eggs.
5. Designate a Sacrificial Tomato Plant
This is another place where overplanting comes in.
Plant an extra tomato plant, maybe two, and know from the start that if hornworms appear, this is where they will go. When you find hornworms, move them to the sacrificial plant.
This is along the lines of keeping trap crop plants...except that you assume the moths will lay eggs wherever, and you will relocate the caterpillars to a better place you both can be happy with.
This is a no-kill option, and you won’t have to stress because this was the plan all along.
If you didn’t plan ahead to overplant, decide if you can spare a plant in your patch, make that the hornworm designee, and go from there. Maybe you'll even get lucky and still have some tomatoes from that plant left for you.
You could also combine this method with covering your tomato patch with a row cover. Cover all the plants but the one or two sacrificial plants you plan to keep, and let the moths lay eggs there.
Do keep a good eye on tomato plants that are close to the trap crop plants/sacrificial tomatoes. If leaves touch, the caterpillars could use that as a pathway for travel.
It would be best if your sacrificial tomato plant is planted a distance away from the patch you’re protecting so the caterpillars don’t crawl back over to adjacent plants.
6. Move Hornworms to a Different Host Garden Plant
We’ve mentioned that hornworms will feed on other solanaceous garden plants. If you don’t feel you have the tomato plants to spare, perhaps you have enough extra of a different plant where you’d be willing to let hornworms live.
Other common garden plants that hornworms will feed on are
- Tobacco
- Peppers
- Eggplant
- Potatoes
If you’ve never seen hornworms on these plants before, it’s because tomatoes are their favorites, but if you move the caterpillars to any of these plants, they will stay and complete their lifecycle there.
7. Till Tomato Patches Before Winter
How does this help?
Tilling the soil where tomatoes and other host plants were grown, and where you know hornworms were, is a future population control strategy.
At the end of the season, the caterpillars will drop to the ground, burrow in, form cocoons, and spend the winter in their pupal stage, turning into adult moths in the spring. The moths will then lay eggs and start the lifecycle anew.
When you till the areas where hornworms are overwintering, you reduce their population by up to 90%. This lends good balance and may keep the population low enough to where you can (be grossed out but) live with them.
If you don’t like to till your garden, consider at least tilling the area where you grew plants that had hornworm caterpillars on them.
We Can Live with these Weird Worms and Have Our Gardens, Too
It is possible to live with hornworms in the tomato garden. Every gardener does have to make their own decisions, though. These will be based on various factors and past experience. Some things to consider are
- How heavy is the hornworm population in your garden?
- What is the extent of the damage you are seeing?
- Can your tomatoes (or other garden plants) keep pace with the feeding and growth of the hornworms?
- Would letting this generation live cause an explosion in the next generation?
- Are there are natural forces coming into play that might help mitigate the size of the hornworm population and the damage they are doing? (Birds and parasitic beneficial insects, for example)
- What are your feelings regarding the importance of hornworms and their adult version, hawk moths?
- How large of a crop of tomatoes do you need – is there enough to share?
- How heavily are you relying on your tomato crop as a food source and also on other garden plants that could become infested?
- Could you strike a reasonable balance, a compromise that allows for a limited population of hornworms and hawk moths to coexist with your garden and your garden goals?
There isn’t really a right or wrong answer to these questions. These are questions that can help you decide how to handle hornworms in your tomato patch.
Once you’ve decided how you want to handle living with hornworms (or not), you can revisit your options above and make a plan of action.
If part of that action includes measures to control hornworms, see these articles on Tips for Dealing with Hornworms and Organic Products and Solutions for Hornworm Control.
