Hornworms


What is a Hornworm?

There two major species that are referred to by the name “hornworm.” These species’ scientific names are Manduca quinquemaculata and Manduca sexta. This species is harmless to humans – although it is a well-known pest throughout the US, where they are native to. Luckily, they have not quite reached the point of creating significant economic damage to crops across the country and are typically only the bane of the hobbyist or small-space gardener. One of their names, the tomato hornworm, tells it all. This hefty caterpillar is most recognized for targeting tomatoes but will also feed on other vegetables in the nightshade family, including eggplants, peppers, and potatoes. In one year, there may be two generations to pass through one crop.


They are large species of caterpillar, reaching lengths of up to 4” long. Depending on the species, the hornworm’s body may be white to yellow with no markings, or a beautiful, rich green with intricate designs decorating their sides. Generally, more mature caterpillars in both species can be green with eight V-shaped, white marks with gray and black circles nestled into the point of the white V.


Hornworms get their name from the large horn on the end of their tails, typically black or red, used as a formidable defense against predatory species. If it feels it must defend itself, the hornworm will lift its backside and wave its horn from side to side. Surprisingly, though, this isn’t always their first line of defense. Hornworms, when threatened, will rear up on the posterior half of their bodies in a defensive display (and, from personal experience, it’s quite startling!).


As one of the largest known caterpillars, hornworms – in addition to their impressive length – can weigh up to 0.35 oz (for a larval stage, that’s quite heavy)! These insects, like many species’ larvae, are specialized herbivores, feeding on the leaves of the nightshades mentioned above. Because of how much food they take in – some feed nonstop throughout both days and nights! – their digestive system comprises more than 50% of their body. Normally, they only stop feeding when they molt as they grow through their immature life stages. Under the right environmental conditions, hornworms may reach up to 10,000 times their original weight in as little as two weeks.


The hornworm is not its own, distinct species, however. Rather, it is the juvenile stage of the hummingbird moth, also known as the sphinx moth and hawk moth (other species’ names are tobacco hornworm and goliath worm). These are large, bulky insects with relatively narrow front wings – and very large with a wingspan of 4-5 inches. They may also be some of the cutest of the currently known moth species, with their short, fuzzy bodies and fluffy antennae that stretch far out from their faces. Even in this adult stage, the hornworm is quite aesthetically pleasing, still being covered in designs of gray, brown, black, green, red, or yellow.


As adults, they no longer feed on leaves, but drink the nectar of flowers instead, using their 14” long proboscis (this is what gives them the name “hummingbird moth”). The long proboscis allows the moths to reach deep into the corollas of flowers, enabling the insect to feed on flowers that even butterflies and bees cannot reach.


This moth, among all of its other stunning features, is a fast and powerful flier. During flight, they maintain a body temperature of nearly 100°F – quite high for such an insect. That said, when it is cold outside, moths may prepare for flight by vibrating their flight muscles as a way to build up heat before they take off. This is a form of thermoregulation, another trait that sets these moths apart from many other insect species.


Life Cycle of Hornworms

The hornworm, just like all other moths, goes through a complete metamorphosis as it matures. This means that each life stage preceding the adult moth is unrecognizable and physiologically distinct from each other. There are four stages of the hornworm life cycle: the egg (also known as the “ova”), larvae (once it gets to the more mature end of the larval stage, it becomes known as the caterpillar that most people are familiar with), pupa, and adult.


  • Egg: After emerging in the spring, the adult moths mate and the female deposits her smooth, light green eggs – each about 0.04” in length – individually upon the upper and lower surfaces of solanaceous (nightshades) plants’ leaves. This is done at night, presumably, so the eggs do not desiccate as they are freshly laid. The eggs are quite beautiful to look at, having a pearly sheen about them in addition to the yellow-green or light green coloring.

  • Larva (caterpillar): Once hatched, the larvae do not leave the leaf they were deposited on. Instead, they remain here and feed on the leaf’s tissue as they grow into the following larval stages, known as “instars.” As they grow, the larvae move throughout this original host plant until they reach the fifth instar (the “caterpillar”). Note that, if necessary, they are entirely capable of migrating to another host plant. Otherwise, they risk wasting precious energy stores and may die if they move to a less nutritious source. As larvae, they are incredibly well camouflaged on the leaves of nightshades, making them difficult for even the most attentive gardener to spot. The entire larval stage, comprised of about 5-6 instars, takes about 3-4 weeks.

  • Pupa: When they are ready to pupate, the larvae will drop off of their host plant and burrow into the soil below. Hornworm pupae are markedly different in appearance to the caterpillar. Instead of a rich green with beautiful decorations, they darken to a deep reddish-brown and have a loop at the anterior end (this becomes the mouthparts of the adult moth). The pupae remain in the soil for about 2 weeks until they are ready to emerge as adult moths.

  • Adult: During the spring, the adult moths begin to emerge from the soil in their final, beautiful form. They may be patterned in many striking colors mentioned above and are relatively heavy and large for a moth. During their adult lives, they focus primarily on mating and reproduction.


Where Are Hornworm From?

There are more than 1200 known species of hornworms throughout the world, with high levels of diversity in tropical regions. In the US, there are approximately 120 species that are native to many states across the country, mostly distributed throughout the Northern states.


Nutritional Value of Hornworms

Hornworms are a great feeder species to feed your beloved reptile. Since they have no hard exoskeleton, they’re great for animals that may have difficulty in digesting their food, especially for younger reptiles that are just getting the hang of feeding. They also provide a great deal of moisture for any reptile that may be suffering from dehydration.



Nutrient

Percentage in Hornworm

Moisture

85

Protein

9

Fat

3

Calcium

4.6



How to Raise Hornworms

Hornworms are very easy critters to raise. Given that they exist so often in human-dominated landscapes, such as farms and home gardens, they are not too demanding in captivity and can be easily satiated with foods you may already have readily available. Still, it is not recommended that you just pick up any old hornworm from outside your house, as you cannot be sure of what diseases it may harbor. Instead, order hornworms from a reputable breeder to ensure the highest quality feeder for your reptile. Below are some guidelines to help you get started in raising hornworms.


1. Housing Your Hornworms

When you order your hornworms, they will arrive in a plastic cup with only a little bit of substrate covering the bottom of the cup. Although the larvae can persist in this container for several days, you should separate each larva into individual containers as soon as you can. This is to ensure the best, healthiest growth rates for each of them as you will be protecting them from competing for food. Do this carefully, though! Since they are so soft, lacking the chitinous outer covering that many other feeder insects have, they can be more easily damaged during handling.


Once separated, place each hornworm into its own vial with a pre-made, artificial diet. (You can feed them kitchen scraps, but, due to the moisture content of the types of vegetables they eat, and therefore, their propensity to rot quickly, it may be in your best interest to primarily offer dry food.)


2. Maintenance

You must provide your hornworms with a constant light source to keep them happy and healthy. Keep them at a temperature of 81°F, and never allow their containers to get too close to, or surpass 90°F, as this will surely kill them. Feed them once daily with your artificial feed, and they will remain healthy and nutritious for your lizard or turtle!


Hornworms are a highly nutritious supplement for your reptile and are packed with moisture, great for any animals that may struggle with their water intake. They’re also a great snack for picky eaters and are incredibly easy to find and raise. This beautiful insect can be a unique addition to your reptile’s diet, and a rewarding critter to maintain.