Atteva numeratrix, commonly known as the Ailanthus webworm moth, is a species of moth belonging to the family Attevidae (formerly placed in Yponomeutidae). It is notable for its distinctive appearance and its strong association with the invasive tree-of-heaven, Ailanthus altissima.
Description
The adult Atteva numeratrix is a strikingly colorful moth. Its wings are typically bright orange to reddish-orange, adorned with a complex pattern of metallic black or dark blue-black spots and bands. The pattern can vary somewhat among individuals, but the overall coloration makes it quite conspicuous. Its wingspan ranges from approximately 25 to 35 millimeters (1.0 to 1.4 inches). The larvae, or caterpillars, are pale yellow-green with several small, black spots and sparse hairs. They are gregarious, living and feeding communally within silken webs they construct on their host plants.
Taxonomy
Atteva numeratrix was first described by Johan Christian Fabricius in 1787. It is classified within the genus Atteva, which comprises a group of moths known for their bright coloration and often diurnal (day-flying) habits. Historically, the genus Atteva was placed in the family Yponomeutidae, but recent phylogenetic studies have led to its reclassification into the separate family Attevidae.
Distribution
This species is native to North America, primarily found throughout the eastern United States and southeastern Canada. Its range has expanded and shifted somewhat in correlation with the spread of its primary host plant, Ailanthus altissima.
Life Cycle and Host Plants
The Atteva numeratrix is polyvoltine, meaning it has multiple generations per year, particularly in warmer climates. The moths typically emerge in spring, mate, and lay eggs on the leaves of host plants. The larvae hatch and begin to construct silken webs, within which they feed on the foliage. These webs can sometimes enclose entire branches or small trees. After completing their larval development, they pupate within the web or in leaf litter nearby. Adults are often seen flying during the day, especially in sunny weather, and are attracted to lights at night.
The primary host plant for Atteva numeratrix is the tree-of-heaven (Ailanthus altissima), an invasive species introduced to North America from Asia. While Ailanthus altissima is its most common host, particularly in areas where it is abundant, the moth also feeds on native sumac species, such as smooth sumac (Rhus glabra) and staghorn sumac (Rhus typhina). The larvae are one of the few native North American insects that have successfully adapted to feeding on the chemically defended Ailanthus altissima.
Ecological Significance
Atteva numeratrix plays an interesting ecological role, particularly in relation to its association with Ailanthus altissima. Because A. altissima is a highly invasive and often problematic species in North America, the moth's herbivory can be viewed as a form of biological control, as its feeding can cause significant defoliation and stress to the trees. However, the damage rarely kills mature Ailanthus trees, and the moth also feeds on native sumacs, which are valued plants. Despite its pest status on Ailanthus, the moth itself is generally considered harmless to humans and domesticated animals. Its vibrant coloration is a form of aposematism, signaling to potential predators that it may be unpalatable due to compounds ingested from its host plants.