The saddleback caterpillar (Acharia stimuli, formerly Sibine stimulea) is the larva of a species of moth native to eastern North America.

During the mid and late instar (a phase between two periods of molting in the development), Acharia stimulea exhibits its characteristic lime-green coloring along the top of the body that contains its most identifiable feature, a dark marking at the center that is inclosed in a white and black that resembles a saddle.

Acharia stimulea are native to North America and are most known for living in warmer climates like Yucatan, Mexico but they can also survive the slightly cooler temperatures of the eastern United States.

[3] Adult moths fly during warm months which can be year round in the south or between July and August in the U.S.[5] Acharia stimulea are polyphagous and do not rely on a single plant species for survival though they tend to favor palms.

[3] While pupating the cocoon appears to be a hardened light brown spherical shape with black veining that is encompassed in silk webbing.

One of the main characteristics of Acharia stimulea at this stage is the presence of white dots that occur with about one or three at the apex and one at the inner middle of the anterior wings.

After mating the female will choose a host plant and lay her eggs on the underside of the leaf where she will frequently visit until they have successfully hatched.

While these spines are threatening alone, they actually go a step further in acting as a defense mechanism as they are connected to a gland that secretes venom that, when broken, is released into predators or unsuspecting gardeners.

[3] Throughout the larvae stage Acharia stimulea also exhibits a false face with two green or white dots that contrast against the dark coloring of the body that act as large eyes.

This is an example of defensive mimicry which can be seen in other moth species such as Deilephila elpenor (elephant hawk-moth) which exhibits snake like features in order to deter predators.

[10] It is not uncommon for these facial features to be represented on the posterior as it is believed to be used to misdirect predators and is often called automimicry or intraspecific mimicry.

[10] Acharia stimulea is known for having one of the strongest stings and, because the saddleback caterpillar is commonly found in ornamental plants, gardeners are most at risk of accidental exposure.

[3] These spines are fragile and can become airborne and embedded into surfaces therefore immediate action is required for removal if infected to prevent prolonged harm.

[3][9] Symptoms can be mild or severe and can last from a few hours to a few days depending on the sensitivity of those infected and can be relieved through prescribed medication on a case-by-case basis.

[11] The parasitic wasp eggs are able to survive by feeding on the inside of the saddleback caterpillar and emerge as larvae by creating holes in the body.