Sesia apiformis

Distinguished from Sesia bembeciformis by yellow (not orange-brown) head and tegulae. Distinguished from actual hornets (Hymenoptera) by moth morphology: two pairs of scaled wings (though largely transparent), filamentous antennae, and lack of constricted wasp waist. Exit holes in poplar trunks (~1 cm diameter) with protruding pupal exuviae indicate presence.

Large clearwing moth with transparent wings due to reduced scaling. Bold black and yellow transverse stripes on abdomen. Yellow head and tegulae (shoulder plates). Distinguished from similar S. bembeciformis by these yellow markings; S. bembeciformis has orange-brown head and tegulae. Wingspan substantial among sesiids.

Woodland habitats. Closely associated with poplar trees, specifically tunneling in wood of lower trunk and roots below bark level. Requires host trees of Populus nigra or P. tremula.

Native to western and central Europe, with scattered records extending east to central Russia. Also native to Middle East. Introduced to North America, established on East coast and Great Lakes region. In United Kingdom, most common in East of England; classified as Nationally Scarce.

Adult flight period mid-June to July. Larval development spans at least two to three years within host wood.

Larvae feed on wood of black poplar (Populus nigra) and aspen (Populus tremula). Adults do not feed; mouthparts reduced or non-functional.

• Populus nigra - larval hostblack poplar
• Populus tremula - larval hostaspen

Eggs laid on host trees. Larvae tunnel in wood of lower trunk and roots for minimum two years, possibly three. Larvae create exit hole (~1 cm diameter) prior to pupation. Pupa uses specialized spines (adminicula) to maneuver close to exit hole. Adult emerges through exit hole; pupal exuviae protrude slightly from hole, providing visible sign of emergence.

Females remain stationary on tree trunks, emitting pheromones to attract mates. Males actively fly to detect female pheromones; upon locating female, male positions himself upside down beneath her for copulation. Adults rarely observed despite large size. Strong flight with hornet-like appearance that deters predators.

Phytophagous wood-borer. Primarily attacks stressed, weakened, or drought-impacted host trees rather than healthy individuals. Limited evidence of significant damage to UK poplar populations; drought-stressed trees can recover even with larval presence. Role in ecosystem as decomposer of compromised wood.

Subject of biological control concerns regarding poplar plantations; historically accused of causing serious damage to hybrid black poplar trees, though research indicates primary impact on already-stressed trees. Genome sequenced (Wellcome Sanger Institute, 2024). Elicits strong emotional response in observers due to hornet mimicry. Unforgettable emergence behavior from tree trunks noted by observers.

• Sesia bembeciformisOverlapping distribution and similar clearwing morphology; distinguished by orange-brown (not yellow) head and tegulae
• Sesia tibialisNative North American congener; may compete with introduced S. apiformis in introduced range
• Vespa crabro (European hornet)Batesian mimicry model; distinguished by Hymenoptera features including constricted waist, elbowed antennae, and two pairs of membranous wings with different venation

Historical attribution of serious poplar tree damage to this species; current evidence indicates larvae primarily colonize trees already weakened by drought or water table impacts, with limited independent capacity to damage healthy populations.

• BugGuide
• GBIF taxonomy match
• iNaturalist taxon
• NCBI Taxonomy
• Catalogue of Life
• The genome sequence of the Hornet Moth, Sesia apiformis (Clerck, 1759).