Hornworms are one of the most dreaded pests of plants from the nightshade family, such as tomatoes and eggplants. But where do hornworms come from? How can you stop them from attacking your plants? Let’s find out.
Surprised to find hornworms all over your tomato plant? Well, both tobacco and tomato hornworm caterpillars are quite common pests, and it isn’t very unusual to find them in your vegetable garden.
You should work on getting rid of these pests without delay because they can defoliate your plant completely in a matter of days.
However, you might be wondering how hornworms got into your garden in the first place. This article addresses this question and will help you understand where hornworms come from.
How To Find Tomato Hornworms
If you’ve found a few hornworms in your garden, the chances are that there are more of them. You can find tomato hornworms by:
- Checking for them visually when they are large enough
- Using a black flashlight
- Looking for their black droppings on leaves
Do keep in mind that the tomato hornworm’s body camouflages it perfectly amidst the foliage, which can make them very hard to spot.
How Do Hornworms Get on Tomato Plants?
Hornworms can’t fly around until they’ve matured into adult moths. This might make you wonder how they got on your tomato plants.
Well, here’s the thing – the worms didn’t move to your tomato plant; they were born on it. Hornworms are born from eggs laid by adult female sphinx moths (also known as hummingbird moths).
Moths lay their eggs directly on a host plant so that the hornworm larva has an ample food source when the egg hatches.
Tomato plants are among a hornworm’s favorite food sources. Moths often lay their eggs on tomato plants, on the undersides of the leaves.
Since they are hidden underneath, you might not notice them until they hatch and become large enough. The eggs will hatch within 3-4 days, releasing baby hornworms all over your plant.
Each moth can lay as many as 1000 eggs within its lifetime, so you will suddenly find hordes of tomato hornworms eating your precious plants.
Hornworms can also get on a tomato plant by crawling to it from a nearby host plant. However, they don’t usually leave their original host until they have reached the advanced larval stages.
How To Identify Tomato Hornworms
Although tomato hornworms are hard to spot due to their green color, they’re easily identifiable. In the larval stage, i.e., while existing as worms, these garden pests have a body structure very similar to butterfly caterpillars.
Their color usually varies between light green and yellow-green, just like the leaves of the plants they tend to infest. Additionally, they also have V-shaped white stripes on their bodies.
However, despite their similarities to other caterpillar species, tomato hornworm caterpillars have a distinct identifying feature – their horn.
A black, horn-like structure protrudes from their rear. The horn is just ornamental – the hornworm uses it to try and scare away predators. However, neither is it venomous nor is it hard enough to hurt you in any way.
Full-grown tomato hornworms are around four to five inches long, which makes them one of the largest caterpillars in the world.
Tomato vs. Tobacco Hornworms
Tomato and tobacco hornworms are the two most common hornworm species found in North America.
The two are very similar to each other, including the fact that both species can cause heavy damage to crops and vegetable gardens.
However, there are a few identifying features that can help you differentiate between the two:
- Color of the horn: The horn on the back of a tomato hornworm is black or bluish-black. Tobacco hornworms, on the other hand, have red horns.
- Stripe pattern: The two species of hornworm also have different stripe patterns. While the tomato hornworm has V-shaped stripes, a tobacco hornworm features parallel and slanting stripes.
- Black spots: Unlike tomato hornworms, tobacco hornworms have a black spot lining each stripe. Tomato hornworms don’t have any such spots.
Despite the difference in their names, tobacco hornworms are as disastrous to your tomato plants as the tomato hornworms.
Recognizing hornworm damage
Recognizing the damage caused to your plants is one of the first steps of pest control. You should start looking for signs of damage on your plant as soon as you notice these destructive pests.
Hornworms feed on their host plant right from the beginning of their larval stage, so you might find leaves that are partially or completely missing in just a few days after spotting a hornworm.
Start by inspecting the leaves at the top of the plant – that’s the area hornworms tend to attack first. The most obvious sign of hornworm damage is a bald petiole near the top region.
Besides tomato and tobacco plants, these pests also target other plants of the nightshade family, such as eggplant, potato, and pepper.
How To Get Rid of Tomato Hornworms?
Thankfully, getting rid of hornworms isn’t too difficult. There are plenty of solutions, including natural ones that won’t require you to use chemical pesticides.
You can simply remove the worms by picking them with your hands.
Another effective long-term strategy is to bring in beneficial insects like green lacewings, ladybugs, and parasitic wasps. These predators prey on hornworms, and they will soon rid your garden of these pests.
The braconid wasp is particularly good at keeping hornworm populations under control.
Other methods include crop rotation and the use of Bacillus Thuringiensis-based pesticides, Cayenne pepper spray, neem oil, Spinosad, etc.
Frequently Asked Questions
How are hornworms born?
Hornworms are born as tiny, green eggs laid by a sphinx moth (or hawk moth or hummingbird moth, whichever name you prefer). The green hornworms you see on your plant are actually in the larval stage of their life cycle. As the larval stage ends, they pupate and transform into moths that lay eggs.
Where can hornworms be found?
Hornworms are very common pests that feed on plants of the nightshade family. If you farm tomatoes in your vegetable garden, you’ll likely encounter them at least once. You may also find them on a potato, eggplant, or tobacco plant.
How do hornworms get in your garden?
Unless you brought in a plant infested with hornworms, it’s unlikely that the pests’ got in your garden. Rather, they were probably born in your garden, hatching from eggs laid earlier by a hornworm moth.
The moths lay their eggs on a suitable host plant so that the newborn larvae have enough food available to them.
What do hornworms turn into?
Hornworms belong to a family of moths called Sphingidae. This means the worms are just larvae that later mature into hummingbird moths.
At the end of the larval stage, a hornworm falls to the ground and burrows itself to start pupating. About two to four weeks later, the adult moth emerges.
Well, now you know where those pesky hornworms in your vegetable garden came from. We also talked about the ways to get rid of hornworms. You can try these methods to fix your hornworm problem.
Hopefully, you’ll be able to eliminate those pests without much trouble and protect your plants from them in the future.
Over the years, our readers have sent us several emails on this topic. Please go through them below.
Letter 1 – Unidentified Hornworm from Mexico
Subject: Moth caterpillar?
Geographic location of the bug: Central Mexico
Time: 08:24 PM EDT
Your letter to the bugman: Hello bugman! I found this beautiful guy while sweeping the back porch. I know he must turn into something gorgeous so I’m wondering what he is, what he eats, and where would be the best place to put him?
How you want your letter signed: Emma
This is a Hornworm in the family Sphingidae, but we are uncertain of the species. We will attempt additional research but we are posting your image in the hopes that one of our readers (Bostjan are you reading?) can provide a species identity. We suspect this individual is pre-pupal and that it was searching for an appropriate location for pupation.
Letter 2 – Unknown Caterpillar from Brazil might be early instar Hornworm
Location: Juiz de Fora / MG / Brazil
February 27, 2013 9:52 am
Hello, I found two caterpillars like this and would like to identify the species in order to breed in captivity
Signature: Raphaela Campos
We believe this might be an early instar Hornworm in the family Sphingidae. We will check with Bill Oehlke.
Bill Oehlke concurs
I suspect one of the Isognathus species of Sphingidae
I would be happy to try to help the photographer with rearing instructions
if he/she would like to try to rear it through to adulthood and provide
images of the various stages along the way. I would have a better chance of
doing the id with image of mature larva or moth. Feel free to give
photographer my email and the info above.
Letter 3 – Unknown Hornworm from Florida from genus Erinnyis
Subject: caterpillar ID
Geographic location of the bug: St Petersburg FL
Time: 02:03 PM EDT
Your letter to the bugman: Hi, I was just hoping you might be able to help me identify this large caterpillar found on my fence this morning
How you want your letter signed: Thanks, NAS
This is a Hornworm, the caterpillar of a Sphinx Moth in the family Sphingidae, but we are uncertain of the species. Though your individual reminds us of the Hornworm of a Ficus Sphinx, it is not one of the typical color variations we see in that species. Perhaps one of our readers will be able to provide a species identification
Update: November 1, 2018
We received several comments indicating this is a member of the genus Erinnyis, and Cesar Crash provided this BugGuide link to the Alope Sphinx larva.
Letter 4 – Hornworm from Hawaii: Pink Spotted Hawkmoth Caterpillar
Location: Honolulu Hawaii
January 21, 2011 7:04 pm
What’s the name of this caterpillar or the butterfly/moth that it will turn into? Never seen one like it in Hawaii. It was about 3inches long and cruising down a hiking road.
We actually thought this was going to be an easy identification because this caterpillar is so distinctive and because we know that it it a Hornworm in the family Sphingidae. The Sphingidae of the Americas website allows us to search by state, and we know Hawaii does not have many species, but alas, several of species and subspecies listed in Hawaii are without photos. Bill Oehlke who authors the website notes: “Manduca blackburni, Tinostoma smaragditis, Hyles calida calida, Hyles calida hawaiiensis, Hyles wilsoni perkinsi and Hyles wilsoni wilsoni are endemic species/subspecies (found only on Hawaii).” Your caterpillar reminds us of members of the the genus Hyles of which there are several species and subspecies in Hawaii, though we would not dismiss the possibility that it might be an unusual color variation of the caterpillar of the Pink Spotted Hawkmoth, Agrius cingulata, which is also found on Hawaii. You can note the similarities to the caterpillar of Hyles lineata on the Sphingidae of the Americas website. The more we ponder this, we are leaning toward this being an unusual color variation of the caterpillar of the Pink Spotted Hawkmoth, Agrius cingulata, because of the markings on the head. The examples of the Pink Spotted Hawkmoth Caterpillar on the Sphingidae of the Americas website have decidedly different colors and markings than your individual, but that is still our best guess. We are going to enlist the assistance of Bill Oehlke on this query by copying him on our reply. We suspect he may request permission to post your photo to his website as well.
confirmation from Bill Oehlke
You are correct. It is the highly variable Agrius cingulata.
Letter 5 – Hornworm from India is Oleander Hawkmoth
August 22, 2009
Found in the garden on 12.12.08. Approx 10cm Long and 1.5cm dia.
Can you identify it and tell me what it has by now become? We put it over the wall onto an adjacen vacant plot of land. Haven’t seen any more
This is a Sphinx Moth Caterpillar or Hawkmoth Caterpillar in the family Sphingidae. These caterpillars are often called Hornworms for obvious reasons, and they are harmless. The coloration of your specimen indicates that it was probably getting ready to pupate, which they do underground. We will put in a quick inquiry with Bill Oehlke to see if he recognizes the species, and perhaps one of our readers will write in with a species identification.
Identification courtesy of Karl
August 24, 2009
Hi Daniel and Roy:
This looks like the caterpillar of the Oleander Hawkmoth (Daphnis nerii). It is native to southern Europe, Africa and Asia but is popping up worldwide as its host plant (Oleander) is spread as a popular ornamental. They are apparently well established in Hawaii for instance. The mature larvae are usually green but it does come in a variety of color variations; this is a brown form. The adults are very well represented on WTB and there has been at least one posting of a brown form caterpillar. Regards.