The Ultimate Imperial Moth Caterpillar Diet Guide: What They Eat to Thrive!

The imperial moth ( Eacles imperialis ) is a large and striking member of the Saturniidae family, also known as the giant silkworm moths. While the adult moth is famous for its impressive size and beautiful coloration, the imperial moth caterpillar, or larva, also plays an important role in the moth's life cycle. This article delves into the diet of the imperial moth caterpillar, exploring its food preferences, growth stages, and other interesting facts.

Identifying the Imperial Moth Caterpillar

The caterpillar of the imperial moth, though sometimes difficult to spot, is a fascinating creature. It can grow up to four inches long, roughly the size of an average person's thumb. Imperial moth caterpillars exhibit two primary color variations: green and dark brown.

Diverse Diet of the Imperial Moth Caterpillar

The imperial moth caterpillar is known to consume a wide variety of plants. While it most commonly feeds on pine, its diet also includes foliage from trees such as hickory, persimmon, sweetgum, elm, oak, maple, beech, cypress, and red cedar. This diverse diet allows the imperial moth to thrive in various environments, from deciduous to coniferous forests.

However, the caterpillar diet of E. i. Pini is an exception.

From Egg to Pupa: The Caterpillar's Life Cycle

The life cycle of the imperial moth caterpillar consists of several distinct stages. The eggs, oval-shaped and flattish, are laid singly or in small groups on both sides of the host plant leaf. Initially white, they become transparent, allowing the caterpillar to be seen within. The caterpillar that hatches from the egg is only about 0.39 to 0.59 inches in size, is orange and has black bands and prominent black bristles.

Instars: The Caterpillar's Growth Stages

Imperial moth caterpillars undergo five instars, meaning they molt four times before pupating. Each instar is larger than the last, and the caterpillar's appearance changes with each molt.

First Instar: The larvae are orange with black crossbands and have short hairs.
Second Instar: The caterpillar is black, and its bristles are more proportional to its body.
Third Instar: The bristles become shorter, and spiracles become more noticeable along the body segments.
Fourth Instar: The bristles are even smaller, and longer hairs appear. The larva's back legs have armored plates edged in yellow or light brown. The body color can vary, including green, red, cinnamon, tan, burgundy, or charcoal gray.
Fifth Instar: The caterpillar can reach up to 5.5 inches in size.

Throughout these instars, the caterpillars feed by grabbing onto a twig with their legs, especially the back legs called anal prolegs, pulling the leaves or pine needles over their body, and chomping down.

Pupation: Transformation in the Soil

Once the caterpillar reaches its maximum size, it crawls to the base of the tree and into the soil to transform into a pupa. Unlike butterflies that pupate within a chrysalis, the imperial moth caterpillar pupates in the soil without any protective casing. The pupa is dark brown to black, two inches long, and about three-quarters of an inch in diameter, with a pointed tail and a rounded head.

The Adult Imperial Moth

Adult imperial moths emerge in early summer. Like most moths, they are attracted to lights at night. Females are slightly larger than the males and have bright yellow wings speckled with red-brown spots and a horizontal red-brown line across all four wings. The forewings have two small red-brown circles, and each hindwing has a single circle. The male moth is also bright yellow but has considerably more red-brown coloring.

The imperial moth's coloration mimics an autumn leaf, which probably hides it from predators during the day. Its wingspan can be over 6 inches. Because it only lives to reproduce, the lifespan of this lovely moth is ephemeral.

Rearing Imperial Moth Caterpillars

If you find an imperial moth caterpillar, it isn’t difficult to rear it into an adult. If found still feeding on the host plant, place the caterpillar, along with some host plant foliage, in a container with plenty of space and air. Fresh foliage should be provided to the caterpillar daily. Two or three inches of loose, moist soil in the bottom of the container would provide a place for the caterpillar to pupate when the time comes. If the caterpillar is found on the ground, chances are it has completed feeding and is searching for a place to pupate. In this case, place the caterpillar in a container with soil, and it will likely attempt to pupate. If kept indoors, a beautiful imperial moth may emerge during the winter.

Threats to Imperial Moth Caterpillars

Sometimes, the imperial moth caterpillar will be attacked by a parasitic wasp or fly. The larvae of these wasps or flies usually feed inside the body of the caterpillar, and it may not be obvious that the caterpillar has been parasitized.

Distribution and Conservation

The imperial moth is found in deciduous and coniferous forests throughout North and South America, from southeastern Canada to Argentina. There are also populations in the Midwest and the Rocky Mountains, but the moth is mostly found in the mid-Atlantic and southern states of the United States.

Imperial moths aren’t rare, but their numbers are declining in some areas such as New England. Some believe it’s because these moths, like other moths, find artificial lights irresistible. The moths would rather spin around these lights than mate. The light also makes them easily seen by predators such as bats and night-flying birds. Other problems include pesticides and the accidental introduction of diseases.

Interesting Facts about Imperial Moths

The imperial moth's scientific name is Eacles imperialis. The meaning of imperialis is “of the empire” in Latin, but biologists don’t know the meaning or origin of the name Eacles, even though the genus was established by the entomologist Jacob Hübner around 1819.
The imperial moth is one of the most widespread, large, and beautiful of the silkworm moths.
The imperial moth doesn’t eat. Its only job is to reproduce, so its lifespan is usually no longer than a week. When they emerge from the pupa or eclose, their mouthparts are underdeveloped, and they discharge their digestive systems.
The moth, in the order Lepidoptera, was present about 300 million years ago, during the Carboniferous Period, and shared a common ancestor with today’s butterflies.
The imperial moth can be identified first by its large size. It can have a wingspan that’s 7 inches across. Its wings are largely autumnal yellow with splotches, bands, and speckles of pinkish or purplish brown. It often looks like a fading leaf on a poplar tree, and even somewhat mimics the shape of the leaf. The imperial moth has “eyespots” on its wings, and it has a purplish-brown body, a yellowish collar beneath its head, and huge black eyes. Females are larger and fatter, for they are already full of eggs when they emerge from their pupa. Their antennae are also simple, while the antennae of the male are feathered.

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