Caryomyia viscidolium

Distinguished from other Caryomyia species by gall morphology: the sticky, ginger jar-shaped galls on hickory leaves are diagnostic. Similar species C. caryaecola produces smooth, non-sticky galls; C. tubicola produces tubular galls on leaf petioles or midribs. C. holotricha produces hairy, non-urn-shaped galls. Examination of gall surface texture (viscid vs. glabrous or pubescent) and overall shape allows field identification. Adult identification requires microscopic examination of genitalia and is not practical for field use.

Adults are minute flies, typical of Cecidomyiidae, with reduced wing venation and long, bead-like antennae. The species is primarily recognized by its induced galls rather than adult morphology. Galls are small (approximately 3–6 mm), urn-shaped to globular with a constricted opening, greenish to reddish in color, and covered with a viscid (sticky) secretion that gives the species its name. Larvae are small, legless, and maggot-like, developing within the gall tissue.

Associated with deciduous forests and woodlands containing hickory trees (Carya spp.), particularly shagbark hickory (Carya ovata) and bitternut hickory (Carya cordiformis). Galls form on the upper surface of leaflets. The species requires mature hickory stands with sufficient leaf area to support gall development.

Eastern North America, corresponding to the native range of its Carya host species. Documented from the northeastern United States through the Midwest, extending southward along the Appalachian range. Specific state/province records are limited due to the species' recent description and reliance on gall identification.

Adult emergence occurs in spring, coinciding with hickory leaf flush (typically April–May). Gall formation is visible from late May through summer. Larvae develop within galls through summer, with mature larvae exiting galls in late summer to early fall to pupate in soil. Overwintering stage is the pupa in soil.

Larvae feed on nutritive tissue induced within the gall; the plant tissue is modified by larval secretions to form a specialized food source. Adults do not feed or feed minimally on nectar or honeydew (specific feeding habits of adults unconfirmed for this species).

• Carya ovata - hostprimary host, shagbark hickory
• Carya cordiformis - hostsecondary host, bitternut hickory
• Carya - hostgenus-level association with hickories

Eggs are deposited on expanding hickory leaves. Larvae induce gall formation upon hatching, developing through three instars within the protected gall chamber. The gall provides both shelter and modified nutritive tissue. Mature third-instar larvae exit through the gall's apical opening, dropping to the soil to pupate. Pupation occurs in the soil, with adults emerging the following spring. Univoltine (one generation per year).

Larvae are sedentary, remaining within the gall throughout development. The sticky gall surface may function in defense against predators or parasitoids by trapping small arthropods. Adults are weak fliers, typically remaining near host trees. Mating and oviposition occur on or near hickory foliage during the brief adult flight period.

As a gall inducer, modifies hickory leaf tissue, creating microhabitats that may be used by inquilines or secondary occupants. Galls represent a sink for plant nutrients and may marginally affect host tree fitness, though impacts are generally minor. Serves as prey/ host for specialized parasitoid wasps (specific parasitoids unconfirmed for this species but expected based on family patterns).

Of minor economic significance; galls may cause aesthetic concern but do not substantially harm hickory trees. The species is of interest to naturalists and entomologists studying gall biodiversity. Common name reflects the distinctive appearance that facilitates citizen science documentation.

• Caryomyia caryaecolaProduces similar urn-shaped galls on hickory, but galls are smooth and non-sticky; gall surface lacks viscid secretion.
• Caryomyia tubicolaForms tubular or spindle-shaped galls on hickory petioles and midribs, not on leaf blades; galls are not urn-shaped.
• Caryomyia holotrichaProduces globular, densely hairy galls on hickory leaves; galls are pubescent rather than viscid and lack the ginger jar constriction.

• gall midge
• Cecidomyiidae
• hickory
• Carya
• plant gall
• Caryomyia
• Diptera

• BugGuide
• GBIF taxonomy match
• iNaturalist taxon
• Catalogue of Life