Thursday, July 11, 2024

Tomato Hornworms: A Comprehensive Guide for Gardeners and Curious Minds

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Tomato hornworms appear menacing, even dangerous. That was my first impression, until my husband, using his bare fingers, snagged one from a tomato plant, and squashed it beneath his foot.

Like many gardeners and cultivators of the land, inexperienced or otherwise, you’ve stumbled across this caterpillar, and want to know more about it.

That’s the sole purpose of this article—to share with you everything I know about tomato hornworms through extensive research online and in books (references are added at the end of the article).

In addition, I’ve experienced how voracious and quick these horn-touting, plant-hugging caterpillars can be if left unchecked in your garden.

What are Tomato Hornworms?

Tomato hornworms are given the scientific name Manduca quinquemaculata. The green-hued caterpillar may grow up to 4-inches in length when full maturity is reached.

Some tomato hornworms may develop a brown color, but rarely does this transition occurs.

The Manduca quinquemaculata species of hornworms can be found throughout Central, South and North America, and Caribbean Islands.

The tomato caterpillar has five (5) pairs of abdominal limbs and three (3) pairs of thoracic legs. The most impressive and bizarre feature of the tomato caterpillar is its horn or pointed structure.

The horn is situated on the end of the abdominal area, and is often the same size as a newly emerged larvae. Once maturity sets in, the horn shrinks, or gradually becomes smaller.  

Young tomato caterpillar larvae appear yellowish-white but later transition to a green hue during the second instar.

Tomato Hornworm Life Cycle

Like most moths and butterflies, the tomato hornworm life cycle works just about the same.

The different subheadings to follow detail the different stages the tomato hornworm goes through—tomato hornworm eggs, tomato hornworm larvae, tomato hornworm pupae, tomato hornworm adult.

1. Tomato Hornworm Eggs

Tomato hornworm eggs are globular or round in form, with a diameter measurement of 1.25 to 1.50 mm.

The eggs are silky smooth and covered in differing colors—some yellow and some white—depending on the stage of maturity.

Eggs are principally dropped or dumped onto the lower and upper surfaces of leaves. However, preference is mainly given to lower areas.

On average, between 240 to 360 eggs are deposited, but there may be ebb and flow, depending on the season.

If an adult hornworm receives optimum nutrition, it may be able to deposit up to 1400 eggs (per female).

On average, the egg stage may last 5 days, but often between 2 to 8 days.

2. Tomato Hornworm Larvae

After a tomato hornworm egg hatches, larvae emerge. These are tube-shaped and have eight (8) pairs of legs, with divisions made in the thorax and abdominal regions.

On average, the tomato hornworm caterpillar underdoes five (5) larval stages, but an additional instar (bringing the count to six (6)), is often identified.

An instar may be identified using the size of its head capsule and body length.

Exoskeleton or head capsule of tomato hornworm instars.

  • Instar 1: 0.8 mm (Body Length: 6.7 mm)
  • Instar 2: 1.2 mm (Body Length: 11.2 mm)
  • Instar 3: 2.0 mm (Body Length: 23.4 mm)
  • Instar 4: 3.0 mm (Body Length: 49.0 mm)
  • Instar 5: 5.0 mm (Body Length: 81.3 mm)

Typically, larvae may take up to 20 days to develop, although, with differing temperatures, this could decrease or increase (somewhere between 13 and up to 44 days).

When housed in an insectarium, tomato hornworm larvae may take fewer days to develop.

Development days in an insectarium depending on the instar include 3.4, 2.9, 3.0, 3.9, and 6.6 days.

3. Tomato Hornworm Pupae

Once maturity sets in for a larva, it drops to the soil, where it excavates about 5 inches long and 2 ³/₄ inches wide into the soil. Pupation usually starts between 4 to 8 days and may go beyond 100 days. The duration may also be as short as 15 days, with a mean of 21 days.

A pupa may measure up to 2 ²³/₆₄ inches in length and about 14 mm in width. The chrysalis is often brown to reddish in hue.

Overwintering pupae may not appear at the same time, but extend from May to the early parts of August. Some pupae may also suspend activity for over two (2) winters.

4. Tomato Hornworm Adult

After emergence, the once inactive pupa is now an adult and ready to take flight. The tomato hornworm adult is large, with a wingspan of up to 5.118 inches. Females are bigger than males, and forewings often tower above hindwings.

In addition to identifying a female tomato hornworm adult by its size (in comparison to males), her antennae are much slimmer or narrower.

The exterior of the adult hornworm is a grayish brown (dreary grayish) hue and distinct with five (5) orange-yellow spots. For the back wings, there are varying bright and dark stripes.

Tomato Hornworm Moth

It is said that the tomato hornworm moth produces a sex hormone/pheromone. Some moths can be seen feasting on flowers at sunset when they increase their activity, while others maintain their zeal and liveliness throughout the night.

Some moths will lay eggs for up to 8 days.

Tomato hornworms will make a meal out of solanaceous plants, such as those belonging to the nightshade family. However, the preference seems to be given to tomato and tobacco plants (hence the names tomato and tobacco hornworms (more to come on this)).

Although it happens, feeding on other plants such as peppers, potatoes, eggplants, and other vegetables aren’t customary sightings of the tomato hornworm.

Where tomato hornworm adults are concerned, they can be seen drinking or gulping plant sap from flowers, included but not limited to the catalpa, daylily, mallow, and others.

Tomato Hornworm Control

Tomato hornworm control methods vary. One of the quickest ways to control tomato hornworms during the last instar stage is to watch out for them.

These are often found foraging for food on tomato plants. Although they can be easily picked off tomato crops, as commonly done, sometimes they go unnoticed. This is simply because the insect’s exterior or coating serves as camouflage.

In fact, I’ve had the displeasure (and pleasure) of spotting tomato hornworms on a plant, immediately after it was inspected by my husband.

Simply being on the lookout for these menaces helps, but when tomato caterpillars come out in numbers, you could be picking off more than 4 insects from a single tomato plant. That has been my experience.

If you cultivate tomatoes in dozens, this could be pretty hard work to handle alone. If you have kids, they’ll find the activity of spotting and picking off tomato caterpillars exhilarating.

To this day, I still pick them off with a stick or barrier between my fingers and the caterpillar. I’ve never mustered up the strength or courage to pluck them from a plant with my bare hands (don’t judge me).

1. Tomato Hornworm Control—Larvae

Best controlled through inspection and hand-picking. The soil-dwelling bacterium called Bacillus thuringiensis can be used to reduce the presence of larvae as a biological pesticide.

This can be picked up at some local stores or ordered from Amazon. Adult tomato caterpillars are more difficult to kill.

In addition, attracting paper wasps (Polistes wasps) is another practical option to consider. These devastate tomato hornworms through predation. Another predator of the tomato hornworm larvae (which is said to be more effective) is tachinids. These are small flies that parasitize tomato caterpillars.

Note: The big-eyed bug and Jalysus spinosus are fierce predators of tomato hornworms at the egg stage.

2. Tomato Hornworm Control—Pupa

Since the pupa doesn’t burrow deep within the soil, frequent tilling may also reduce the tomato hornworm population and prevent them from advancing from larvae to adults. Ploughing the soil may cause up to a 90% death rate.

3. Tomato Hornworm Control—Adults

With a strong attraction to light, light traps have been used to lure and capture tomato hornworm adults.

Tomato Hornworm VS Tobacco Hornworm

There are notable comparisons between the tomato hornworm and tobacco hornworm (there are similarities and differences).

Let’s speak, first, on the appearance of the tobacco hornworm (Manduca sexta), since I’ve covered a great deal about the tomato hornworm.

Unlike the tomato caterpillar that has seven V-shaped marks that run horizontally/sideways, the tobacco hornworm has straight white lines that are slanted (usually with shades of black on the top borders).

The horn on the tobacco hornworm also differs from that of the tomato hornworm. The tobacco caterpillar proudly wears its horn red, while its counterpart tends to be black or dark blue (depending on the instar stage).

Both species of hornworms have similar colored exteriors, ranging from light green to sporadic dark brown and black.

Both tomato and tobacco hornworms have similar pupae. However, the maxillary loop in tomato hornworms is longer.

In both adult species, their dominant exterior wears the same hue, although tobacco hornworms have six (6) markings along the abdomen, while the tomato hornworm has 5 spots.

Tomato Hornworm Pictures

To be able to identify the voracious caterpillar, I’ve included some tomato hornworm pictures (tobacco hornworms are included, too). Let me know in the comments section if you can spot the difference.

While some of these tomato hornworm pictures were taken by me, others were taken from stock photo sites like Pixabay, Pexels, Unsplash, and Insect Images.

Frequently Asked Questions About Tomato Hornworms

Can a Tomato Hornworm Hurt You?

When I first saw the frightening horn carried by the tomato hornworm and its fearsome appearance, I thought it was dangerous, even poisonous.

But, my entire disposition changed when my husband started handling them without protection. The truth is the tomato hornworm is harmless. While it carries a horn, it does not sting.

If you find them on your tomatoes or tobacco plants, don’t be afraid to pick them off.

What Does the Tomato Hornworm Turn Into?

Once the tomato hornworm goes through the stages I’ve listed above, it will turn into a moth. Specifically, the tomato hornworm will turn into the five-spotted hawkmoth (Manduca quinquemaculata).

As for tobacco hornworms, they eventually transform into the Carolina sphinx moth. They also go by the name tobacco hawkmoth.

Can you Keep a Tomato Hornworm as a Pet?

Yes, you can keep a tomato hornworm as a pet. However, you need to be able to take care of it. I’d suggest watching the video below for more information.

Bear in mind that these hornworms will eventually metamorphose into adults. That means you need to also learn to take of the insect once it’s in the moth stage.

How Do you Get Rid of Tomato Hornworms?

One of the most effective ways to get rid of tomato hornworms is through frequent inspection of crops. You’ll know when there’s an infestation, as you’ll see the hornworms.

You might also consider buying a tomato hornworm killer on Amazon.

Tomato Hornworms, Conclusion

Don’t be afraid to pick tomato hornworms from your crops. They are harmless and aren’t poisonous. As tomato hornworms are voracious feeders, it’s important to stalk your garden when they’re most active.

If you have any questions, please leave me a message in the comment section and I’ll get back to you.

Samantha Burris
Samantha Burris
Samantha is a writer with an unhealthy fetish for books and a love-hate relationship with insects, bugs, and creepy-crawlies. She enjoys scouting YouTube for vegan videos, and when she’s not chilling with hubby, she’s masterminding the ultimate plan to take over the blogosphere with her wits, creativity, and treasure trove of knowledge. If you’re looking for a conversational and professional scribe, with the ability to compose content across various spectrums, Samantha is your go-to creative.

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