The Life Cycle of the Hornworm

There are two types of hornworm — the tobacco hornworm (Manduca sexta) and the tomato hornworm (Manduca quinquemaculata) — however, the life cycles of both are very similar. Both undergo a complete metamorphosis, transforming from an egg into an adult moth in about thirty days (at temperatures of around 81° F), or up to forty-eight days if the temperatures are lower.

Although the hornworm life cycle is remarkably short, it's quite common for them to produce two generations a year, with many more generations being produced annually in hotter or artificial climates. This makes them great worms to raise if you're looking for reptile food, but perhaps not quite so appealing if you're a tobacco or tomato plant farmer. Either way, let's take a look at the life of the humble hornworm.

Eggs

In late spring, female moths will spend their nights laying eggs on tobacco or tomato plant leaves — depositing eggs largely on the undersides of the leaves in order to protect them from predators. Although the female will only lay between one and five eggs per plant visit, she may lay up to two thousand eggs during her lifetime. The eggs are spherical in shape, approximately 1.5mm in diameter, and vary in color singly from translucent green to off-white. Once laid, the eggs will normally hatch somewhere between two to five days later.

Larvae

After hatching from its egg, the young caterpillar (which will be about seven millimeters in length) will immediately begin to feed on the leaf it was laid on — and it won't stop there. Hornworms have voracious appetites, with a single caterpillar being able to quite easily consume an entire tobacco or tomato plant. This might be interesting to watch if you're breeding caterpillars in a classroom, but if you're a farmer, 'interesting' probably won't be the first word you think of. Incidentally, if you're breeding hornworms at home as reptile food, it's best to feed them an artificial wheat germ diet from the outset, as once a hornworm has tasted natural plant leaves it will rarely return to an artificial food source.

Over the next two to three weeks, the caterpillar will grow considerably. As it does, it will pass through five separate stages (known as instars), shedding its skin and growing a new, larger one on each occasion. By the time it reaches its final instar, the caterpillar will be up to seventy millimeters in length. It will be bright green if bred in the wild, and a distinct turquoise shade if bred domestically (due to the fact that wheat-germ-based diets contain very little pigment).

Further to its color, a dark line will begin to appear down the length of the caterpillar's body during its final instar. This is the caterpillar's dorsal aorta becoming visible, and once it starts to pulsate, the caterpillar will be ready to pupate. Pupation requires darkness, and in the wild, a caterpillar will burrow into the soil. However, if you're raising them at home, place the caterpillar in a small, clean jar and add either potting soil, sawdust, or shredded paper for it to cover itself with. An interesting point to note here is that before the caterpillar pupates, it will shrink considerably as it prepares itself. People often mistake this shrinkage for the caterpillar dying. It's not. So don't throw it out, just let the little thing sleep.

Pupae

Pupation is where the magic happens. Once the caterpillar has secured itself in its underground chamber, its skin will begin to harden into a dark-colored puparium. This process takes about seven days to complete after which the caterpillar will start its transformation.

The amount of time it takes for a hornworm to fully transform into a moth depends largely on the environment. In domestic or artificial conditions, the pupation period lasts about eighteen days. In the wild, however, a pupa can enter a state known as a diapause, where it will delay its rate of development as a response to temperature or weather. Under these conditions, a pupa will remain in a steady state over the winter months, normally emerging as a moth in the spring.

Adults

Having shed its puparium, an adult moth will climb onto a branch and slowly expand its newly-formed wings. With a wingspan of approximately ten centimeters for an adult tobacco hornworm and about thirteen centimeters for a tomato hornworm, they're both quite impressive specimens — the tobacco hornworm, in particular, displaying a remarkable talent for hovering.

With the adult moth's lifespan lasting only weeks, a female is usually ready to mate a few days after it emerges from its puparium. That said, although males may mate several times, a female will only mate once. Mating normally occurs at night, and the process can last several hours (lucky female). After mating, the female will begin laying her fertilized eggs on the undersides of plant leaves, and the whole process begins again.

And so there you have it — from microscopic egg to expert aviator, via a ravenously hungry caterpillar. The hornworm may not be the most popular creature when it comes to farmers, but for the rest of us — especially those with pet reptiles to feed — it's a little green miracle.

Raise your own hornworms

Want to watch the whole cycle happen on your kitchen counter (and feed your reptiles for pennies)? We ship hornworm eggs laid within hours of dispatch, and live hornworms with food included — both backed by our Live Arrival Guarantee.