Acraspis quercushirta

The jewel oak gall is distinguished from other oak galls by its detachable nature, oval shape, and distinctive faceted surface with pointed projections resembling cut gemstones. The gall is found on leaf undersides, specifically along veins. The asexual generation's bud scale galls are inconspicuous and easily overlooked. The species can be confused with A. macrocarpae, but molecular data have confirmed these are the same species; historical separation was based on host records and geographic assumptions.

Adults are small gall wasps typical of the family Cynipidae. The asexual generation females are wingless. The sexual generation produces the characteristic jewel galls: detachable, oval galls (approximately 1 cm or less) with a fissured surface divided into facets that terminate in short, hard points, creating a crystalline or jeweled appearance. Gall color ranges from white to yellowish, tan, or brown.

Associated with white oaks (Quercus section Quercus), particularly in forested and urban environments where host species occur. Found in both natural oak woodlands and areas where white oaks have been introduced as ornamental trees.

North America, primarily east of the Rocky Mountains. Documented in USA: Connecticut, Virginia, Illinois, Michigan, Texas, Utah, Colorado, New Mexico, Oklahoma. Canada: Alberta, Saskatchewan, Manitoba, Ontario, Quebec, New Brunswick. Distribution corresponds closely with the range of white oak hosts, including areas where bur oak has been introduced as an urban tree (e.g., Alberta).

Two distinct adult activity periods corresponding to the alternating generations. Sexual generation adults emerge in late May and early June. Asexual (agamic) females emerge from fallen galls in autumn (fall), then climb oak trees to oviposit in bud scales for the next generation.

• Quercus macrocarpa - hostbur oak
• Quercus gambelii - hostGambel oak
• Quercus chapmanii - hostChapman oak
• Quercus michauxii - hostswamp chestnut oak
• Quercus montana - hostchestnut oak

Alternating generations with complex phenology. Sexual generation: adults emerge late May–early June, mate, and females oviposit on leaf vein undersides, inducing detachable jewel galls. Larvae develop within galls; galls fall with leaves in autumn. Asexual (agamic) generation: wingless females emerge from fallen galls in fall, climb trees, and oviposit in bud scales, inducing inconspicuous galls that overwinter. Development resumes in spring, with adults emerging to complete the cycle.

Asexual females exhibit post-emergence climbing behavior to reach bud scales for oviposition. The species demonstrates precise oviposition site selection: sexual generation on leaf veins, asexual generation in bud scales. Gall induction involves manipulation of plant tissue development, though the specific mechanisms remain unresolved.

As a gall inducer, creates microhabitats that may support inquilines and parasitoids within the gall community. The detachable galls contribute to nutrient cycling when they fall to the forest floor. Part of the diverse oak gall wasp fauna that characterizes North American white oak ecosystems.

No direct economic impact documented. The jewel galls are occasionally noted for their aesthetic, crystalline appearance. The species has been used in molecular studies demonstrating cryptic species resolution and the importance of integrating genetic data with traditional taxonomy.

• Acraspis macrocarpaePreviously considered a separate species based on host and geographic assumptions; molecular data (cytb and ITS2 sequences) have confirmed conspecific status with A. quercushirta. Cytb divergence between regional populations averages 2.08%, comparable to intraspecific variation.
• Other Cynipini on white oaksNumerous oak gall wasps induce galls on white oaks; jewel oak gall is distinguished by its detachable, faceted, vein-based galls with crystalline appearance, in contrast to attached, spherical, or structurally different galls of related species.

• gall wasp
• oak gall
• alternating generations
• agamic generation
• sexual generation
• jewel gall
• white oak
• Cynipini
• North America
• cryptic species
• molecular systematics

• BugGuide
• Wikipedia
• GBIF taxonomy match
• iNaturalist taxon
• NCBI Taxonomy
• The Insects Behind the Weird Growths on Plants