How to identify the Ailanthus Webworm Moth
Though small, this moth is one of the easiest to recognize. The forewings are bright orange divided into four or five cross-bands of black studded with white dots, an unmistakable mosaic. At rest the moth rolls its wings tightly around its body into a narrow tube, so it can be mistaken at a glance for a beetle rather than a moth. Wingspan is only about 1 to 1.2 inches. It is regularly seen by day on flowers, which sets it apart from the many drab night-flying micromoths.
Where it lives
The Ailanthus Webworm is now broadly distributed across the eastern and central US wherever its primary host tree grows. Open GBIF records show the most sightings in Texas, Virginia, Maryland, North Carolina, and New Jersey. It is strongly tied to tree-of-heaven (Ailanthus altissima), an introduced and invasive tree, and the moth's spread has tracked that tree across the continent. Look for adults in gardens, meadows, roadsides, and disturbed urban ground.
When it flies
This moth has a long, warm-season flight. Records peak from July through October, and in the warmest parts of its range it can be one of the last moths still active into mid-autumn. Because it is day-flying, you will encounter it most often on sunny flowers rather than at a night sheet.
Caterpillar and host plants
The caterpillars are gregarious and feed together inside loose silken webs, which is where the webworm name comes from. Their main host is tree-of-heaven (Ailanthus altissima), the invasive tree the moth is named for, and they will also use related plants. Several overlapping generations can run through the warm months in southern areas. While the webbing can look unsightly on a host tree, the moth itself is harmless and is sometimes noted as a minor natural check on an aggressively invasive plant.
How to see one at night
The Ailanthus Webworm Moth is primarily diurnal, so the easiest way to find one is to check flowering plants on a sunny day, especially near stands of tree-of-heaven, from summer into fall. It does come to lights as well, so if you run a night sheet use a UV or mercury-vapor bulb on a warm, still evening; short-wavelength light disrupts moth flight orientation and pulls in far more moths than a white LED. For this colorful little day-flier, though, flower-watching is the surest method. If you are unsure whether the orange-and-black insect you found is this moth, see what moth is this, or check which species are likely near you tonight.
As a reminder, this site does not identify a moth from your photo. It predicts likely species by location and date from open records. For photo ID, try iNaturalist or Seek, BugGuide, the Moth Photographers Group, or BAMONA.