Saddleback Caterpillar: A Vibrant but Dangerous Insect

Meet the saddleback caterpillar, a striking member of the Limacodidae family. Its vibrant colors and unique saddle-like marking will surely caught your eye, but be careful. This tiny species is highly toxic. Its spines can cause severe pain and discomfort. Join me as I delve into the perilous world of the saddleback caterpillar and explore their interesting facts.

Saddleback caterpillar moth
Scientific name: Acharia stimuli
Phylum: Chordata
Class: Insecta
Order: Lepidoptera
Family: Limacodidae
Genus: Acharia

Physical Characteristics

The saddleback caterpillar, known scientifically as Acharia stimulea, is the larval stage of a moth species in the slug moth family. When I first encountered the Saddleback caterpillar (Acharia stimulea), its striking appearance immediately caught my eye. This species is easily recognizable due to its vibrant colors and unique markings. Its body is primarily green, with brown ends and a prominent white-ringed brown dot in the center, resembling a saddle, which gives it its name.

The species has a slug-like body, with a truncated shape and a granulated texture. You can see its fleshy horns at its both ends, covered with urticating (stinging) hairs that can cause severe irritation upon contact​. These are typically orange around the sides, like a skirt, and can be either orange or black on the tentacles at both ends of its body.

Saddleback caterpillar is one leaves

The larvae can grow up to 20 mm (0.8 in) in length, with early instars being around 1.2 mm (0.05 in) and middle instars reaching 5-8 mm (0.2-0.3 in).

The adult moth of the saddleback caterpillar is glossy dark brown with black shading and has dense scales giving them a furry appearance. They have one to three additional white dots on the wings, with the hindwings being paler brown. Its wing span ranges from 2.6 to 4.3 cm, with females being larger than males. With this look, the adult moth is less conspicuous compared to the brightly colored saddleback caterpillar.

Habitat and Distribution

This saddleback caterpillar is found in many parts of North America, predominantly in the eastern United States. You can find them in Florida, Texas,  Kansas, Massachusetts, and Indiana. Its range even extends into Mexico. It thrives in various habitats, including forests, gardens, and parks where its host plants grow.


The saddleback caterpillar has a polyphagous diet, meaning it feeds on a wide variety of plant species. It is particularly fond of ornamental plants and trees. Common host plants include trees (oak, elm, maple, and walnut), shrubs (hibiscus and hydrangea), crops (corn and various vegetable plants), and ornamental plants (palms, especially in regions like Florida and Alabama).

Saddleback caterpillar moth
The adult moth of the species. |Source: Wikimedia

Saddleback caterpillars are toxic

These caterpillars are targeted by many predators including paper wasps, assassin bugs, or braconid wasps. This braconid wasp is a significant threat to saddleback caterpillars. They lay eggs inside the caterpillar, and when the larvae hatch, they start eating the caterpillar from the inside.

To protect themselves from enemies, the saddleback caterpillars apply several defense mechanisms. The first one is vibrant coloration. With a bright green “saddle” on its back surrounded by dark brown at both ends, the species warn predators that they are toxic or unpalatable.

If the aposematic color is not enough, they can use mimicry tactic. The posterior end of the caterpillar has cream or light-green spots that resemble large eyes, creating the illusion of a false face. This defensive mimicry keeps predators away from them.

If these two strategies don’t work, they still have the last card – the hollow, venomous spines at both ends. These spines contain hemolytic and vesicating venom that causes tissue damage. When touched, the spines break off and release venom, causing intense pain, swelling, and sometimes more severe reactions such as nausea or anaphylactic shock. The spines are used defensively by curling outwards so predators cannot avoid them. This formidable defense helps deter predators such as birds and small mammals. The spines are also used in the silk cocoon during metamorphosis to further protect the pupa.

Saddleback caterpillar also poses a risk to humans. If you contact with its spines, it can cause painful stings that lead to redness, rash, and swelling. In severe cases, it may cause systemic reactions requiring medical attention. It’s crucial to handle these caterpillars with care or avoid direct contact altogether. If stung, immediate removal of the spines using adhesive tape and washing the area with soap and water can help mitigate the symptoms​.

Life cycle

The life cycle of the Acharia stimulea consists of four stages: egg, larva, pupa, and adult moth. The female moth lays clusters of 30-50 eggs on the underside of host plant leaves. These eggs are small and transparent and yellow in color with thin edges.

After about 10 days of incubation, the larvae hatch and go through several molts, during which their distinctive saddle markings become more pronounced. The larval stage is the longest, lasting several weeks to 4 or 5 months, during which the caterpillar feeds voraciously.

Eventually, the caterpillar spins a silk cocoon to pupate. In temperate climates, the pupal stage can last several months, during which the caterpillar transforms into a dark brown moth with velvety wings. In tropical regions, this process is faster. The lifespan of this moth is is relatively short, lasting only a few weeks during which the moths mate and lay eggs to start the cycle again.



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