Colopha ulmicola

The presence of red, cockscomb-shaped galls on American elm leaves is diagnostic. These galls are unique in shape—resembling a rooster's comb—and typically appear on leaf veins. Later in the season, galls split open on the undersurface to release winged aphids. The autumn flight of hundreds of tiny insects around elm trees is a conspicuous sign of this species.

Tiny soft-bodied aphid, typically pale to dark in color. Winged sexual forms are observed in autumn migrations. The species is most readily identified by the distinctive gall structure it induces rather than by direct examination of the insect itself.

Associated with American elm (Ulmus americana) as the primary host, and various grasses as secondary summer hosts. Requires mature elm trees for gall formation and grassy areas for summer root-feeding stages.

Eastern North America; documented from Vermont and surrounding regions in the United States. Associated with the native range of American elm.

Eggs overwinter on elm bark. Nymphs hatch in spring when leaf buds break, inducing galls on expanding leaves. Galls mature through spring and early summer; winged forms exit in summer to migrate to grass roots. Sexual winged forms return to elm in autumn (late September to October) to mate and lay overwintering eggs.

Phloem sap feeder. Nymphs feed on undifferentiated leaf tissue within elm galls in spring; summer generations feed on grass roots underground.

• Ulmus americana - primary hostGall formation on leaves; overwintering site
• Grasses - secondary hostRoot-feeding during summer generations

Complex holocyclic life cycle with host alternation. Overwintering eggs hatch in spring; fundatrices induce galls and reproduce parthenogenetically as stem mothers, producing hundreds of offspring within the gall. These develop into winged forms that migrate to grass roots for summer. Cooler temperatures trigger production of sexual forms that fly back to elm in autumn, mate, and females deposit single large eggs under bark flaps to overwinter.

Nymphs secrete chemical compounds that co-opt plant genetic machinery to induce gall formation. Winged sexual forms engage in conspicuous autumn aerial migrations, filling the airspace around elm trees on bright afternoons. Stem mothers reproduce parthenogenetically within the protected gall environment.

Minor plant parasite that typically causes no significant harm to healthy elm trees. Gall formation represents a form of plant manipulation for insect shelter and nutrition. Honeydew production within galls may support other organisms, though specific mutualisms are not documented.

Primarily of aesthetic and educational interest. Galls may cause minor cosmetic damage to ornamental elms but do not require remediation. Autumn flights of sexual forms can be conspicuous around residential trees. No economic or medical significance.

• Other gall-forming aphidsMany aphid species induce galls, but the cockscomb shape on elm is distinctive to Colopha ulmicola
• Phylloxera speciesRelated gall-forming sternorrhynchans with similar life cycles, but induce different gall morphologies on different hosts (e.g., hickory)
• Other Colopha speciesCongeneric species may exist but are distinguished by host associations and gall morphology

• gall-forming
• aphid
• elm
• host-alternation
• parthenogenesis
• plant manipulation
• seasonal migration

• BugGuide
• GBIF taxonomy match
• iNaturalist taxon
• NCBI Taxonomy
• Catalogue of Life
• Archive — Bug of the Week
• Gall darn it! Gall insects on hickory, oak, and elm, Phylloxera caryaecaulis, Andricus palustris, Colopha ulmicola — Bug of the Week
• When aphids fill the air: Elm cockscomb gall aphid, Colopha ulmicola — Bug of the Week
• Sunny with a chance of aphid flurries: Elm cockscomb gall aphid, Colopha ulmicola — Bug of the Week