Cinnabar Moth

Tyria jacobaeae — the cinnabar moth — is one of the most striking day-flying moths in Europe and one of the most-cited examples of biological control of an invasive weed in modern conservation entomology. The species is native to temperate Europe (where it is one of the most familiar day-flying moths in summer meadows) and has been intentionally introduced to North America (especially the Pacific Northwest), Australia, New Zealand, and South Africa as a biological control agent against tansy ragwort. Adults are 3-4 cm wingspan with the species' diagnostic coloration: brilliant CRIMSON-RED-AND-BLACK FOREWINGS — black ground color marked by two crimson red spots and a long crimson red stripe along the wing margin, plus crimson red hindwings. The bold red-and-black coloration is APOSEMATIC (warning coloration) — adults sequester PYRROLIZIDINE ALKALOIDS (PAs) from the larval host plant (tansy ragwort) and retain the toxicity through pupation, making adult moths CHEMICALLY DEFENDED against bird and small-mammal predators. The species is one of the few day-flying moths in NA Lepidoptera (most moths are nocturnal — cinnabar moths are active and flying during full daylight), and the bright flight is one of the most-photographed events in European summer meadow natural history. The species is the FOUNDATIONAL CASE STUDY in BIOLOGICAL CONTROL OF AN INVASIVE WEED in modern conservation entomology. TANSY RAGWORT (Senecio jacobaea) is a toxic European biennial wildflower that contains pyrrolizidine alkaloids — compounds that cause progressive LIVER DAMAGE in cattle, horses, and other livestock that consume the plant in pasture or contaminated hay (with cumulative toxicity that can cause death after months of exposure). Tansy ragwort was accidentally introduced to NA in the early 1900s and became established as a major invasive weed across the Pacific Northwest US, British Columbia, and parts of California — causing tens of millions of dollars in livestock losses annually by 1960. CINNABAR MOTHS WERE DELIBERATELY INTRODUCED from Europe to NA (1959 to British Columbia, then to Oregon and elsewhere) and Australia (1934 onwards) as biocontrol agents against tansy ragwort. Larvae are bright BLACK-AND-YELLOW STRIPED CATERPILLARS (gregarious in early instars, often clustered together in dense groups on host plants) that feed exclusively on ragwort leaves and can completely defoliate large ragwort populations. The combined action of cinnabar moths and the closely-related RAGWORT FLEA BEETLE (Longitarsus jacobaeae — also introduced as biocontrol) has dramatically reduced tansy ragwort populations across western NA and Australia — one of the most successful weed-biocontrol programs ever attempted. The species is harmless to humans and is one of the most-photographed European day-flying moths in summer meadow nature photography.