The garden tiger moth or great tiger moth (Arctia caja) is a moth of the family Erebidae. Arctia caja is a northern species found in the US, Canada, and Europe. The moth prefers cold climates with temperate seasonality, as the larvae overwinter, and preferentially chooses host plants that produce pyrrolizidine alkaloids. However, garden tiger moths are generalists, and will pick many different plants to use as larval host plants.
The conspicuous patterns on its wings serve as a warning to predators because the moth's body fluids are poisonous. Their effects are not yet fully known, but these toxins contain quantities of neurotoxic choline esters which act by interfering with the acetylcholine receptor. The colours are also ideal for frightening predators such as small birds—the moth normally hides its hindwings under the cryptic forewings when resting.
Between stored toxins, conspicuous warning coloration, and sound cues that are generated mostly as a response to bats, A. caja clearly presents itself as an inedible target for predators.
The garden tiger moth has a wingspan of 45 to 65 millimeters (1.8 to 2.6 in). The design of the wings vary; the front wings are brown with a white pattern (which is sometimes missing), the back wings are orange with a pattern of black dots. There are many aberrations (pattern and colour variants), partly obtained artificially and partly by chance. Oberthür, a French entomologist, mentions about 500 different variants shown in 36 figures. Seitz gives an account of some named aberrations.
