Their wings can also reach a wingspan of  30mm. At this stage "Acharia stimulea" lack envenomation and live 10 days on average. Adult "Acharia stimulea" will mate as soon as two days after emerging from their cocoon and will copulate for up to 24 hours. In the wild mating rituals occur during nights with warm temperatures, which can vary between February and July in the United States. 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. "Acharia stimulea" has two distinct defense mechanisms, aposematism and mimicry. "Acharia stimulea" exhibits aposematic coloring which is a distinct vibrant coloring that represents their toxicity. Along the anterior, posterior and skirt of the caterpillar are tubercles that contain threatening hollow spines. 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. These spines are usually orange along the skirt of the caterpillar and orange or black along the tentacles present at both ends of the body. The larvae will use this defensively by curling outwards so that their spines are unavoidable to a predator. The spines are also used in the silk cocoon to further protect it during metamorphosis. 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. While this marking resembles a face, it is actually located at the posterior of the Saddleback caterpillar. 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. 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. "Acharia stimulea" is known for having one of the strongest stings and due to the saddleback caterpillar being commonly found in ornamental plants, gardeners are most at risk to accidental exposure. The spines along the caterpillar, when broken, will release an irritating toxin into its victims that is known to cause acute urticaria in humans.