The Cinnabar Moth (Tyria jacobaeae) is a striking insect easily recognized by its vibrant red-orange and black coloration. This bold patterning is a clear advertisement in nature, signaling to potential predators that the insect is best left alone.
The Toxicity Status
The direct answer to whether the Cinnabar Moth and its caterpillar are poisonous is yes; they are considered toxic when ingested. This toxicity is a highly effective defense mechanism that makes the insect unpalatable to most birds and other natural predators. The bright, contrasting colors are a classic example of aposematism, which is the biological term for warning coloration. The compounds responsible for this protective measure are present throughout the insect’s life cycle, from the larval stage right through to the adult moth.
How the Toxins are Acquired and Stored
The moth does not produce its own toxins but rather acquires them directly from its primary food source, the Ragwort plant (Senecio jacobaea). Ragwort naturally contains a group of toxic compounds called Pyrrolizidine Alkaloids (PAs). The Cinnabar Moth caterpillar is specialized to feed on this plant, consuming the poisonous material without being harmed by it. The process utilized by the caterpillar is known as sequestration, where it absorbs the PAs and stores them within its own body tissues. These stored alkaloids are then carried over through the pupal stage and remain in the body of the emerging adult moth, turning the host plant’s defense into the moth’s protective strategy.
Identifying the Moth and Caterpillar
Visual identification is straightforward. The adult Cinnabar Moth is a day-flying insect with a wingspan of roughly 32 to 42 millimeters. Its forewings are slate-black, marked with a pinkish-red stripe running down the edge and two matching spots, while the hindwings are entirely red with a black border. The caterpillar is even more distinct, featuring broad, alternating bands of black and yellow or orange across its segmented body. Cinnabar Moth caterpillars are most commonly encountered during the summer months, typically from July to early September, often found in groups feeding heavily on ragwort plants. The adult moths are generally on the wing earlier in the year, from May through July, in open, grassy habitats where their host plant thrives.
Danger to Humans and Pets
The danger posed by the Cinnabar Moth and its larvae is almost exclusively tied to ingestion, particularly the consumption of the PAs they contain. For humans and common pets like dogs and cats, the risk from casual contact is extremely low, as the toxins are not injected and are generally not absorbed through the skin in a harmful form. Acute, accidental consumption of a single caterpillar or moth usually results in mild gastrointestinal upset, such as vomiting, rather than severe poisoning. The true danger from Pyrrolizidine Alkaloids lies in chronic, large-scale consumption, which can lead to cumulative and serious liver damage. This risk is most relevant to livestock, such as horses and cattle, which may ingest large quantities of ragwort, particularly when the dried plant is unknowingly mixed into hay.