Ailanthus Webworm Moth

Atteva aurea — the Ailanthus webworm moth — is one of the most striking small moths in North America and one of the most successful examples of WASP MIMICRY by a moth in NA Lepidoptera. The species is widespread across most of eastern and central North America, the southwestern US, Mexico, Central America, and northern South America. Adults are 2-3 cm wingspan with the species' diagnostic coloration: brilliant ORANGE FOREWINGS marked by bold black-bordered CREAM PATCHES that look like inlay work or stained-glass mosaic — the patches are arranged in 4-5 transverse bands across each forewing; the hindwings are dark gray-brown. The bright orange-and-black-and-cream pattern, combined with the moth's habit of holding the wings folded close to the body in a wasp-like posture when at rest on flowers, makes the species an exceptional WASP MIMIC. Bird and small-mammal predators that have learned to avoid stinging Hymenoptera also avoid the harmless Ailanthus webworm. The species was originally a TROPICAL SPECIES native to Central and South America, where it fed on native PARADISE TREE (Simarouba glauca) — a member of the same plant family (Simaroubaceae) as the invasive ailanthus. After ailanthus (Tree of Heaven, Ailanthus altissima) was introduced to North America from China in 1784 (originally as an ornamental tree at Bartram's Garden in Philadelphia), the moth species progressively expanded its range NORTH from its native tropical range, TRACKING THE SPREAD of ailanthus across North America. The species is now established as far north as southern Canada and as far west as the Pacific Northwest — wherever ailanthus has been planted or has invaded. The species is one of the most-studied cases of HOST PLANT TRACKING in modern biology and is featured in essentially every modern textbook discussion of insect-host-plant range expansion. Larvae feed on ailanthus leaves and construct distinctive 'WEB' SHELTERS — webbing together leaves of the host tree with silk to create small enclosed shelters where the gregarious larvae rest between feeding bouts (the 'webworm' part of the common name). Adults are common nectar feeders on a wide range of flowers (especially goldenrod, asters, and other late-summer composites) and are one of the most-photographed small moths in NA macro nature photography because of the dramatic wing pattern. The species is harmless to humans and a beneficial pollinator.