| Orthonama obstipata | |
|---|---|
| Adult female at Zwaakse Weel (The Netherlands) | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Class: | Insecta |
| Order: | Lepidoptera |
| Division: | Ditrysia |
| Family: | Geometridae |
| Tribe: | Xanthorhoini |
| Genus: | Orthonama |
| Species: | O. obstipata |
| Binomial name | |
| Orthonama obstipata (Fabricius, 1794) |
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| Synonyms | |
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Numerous, see text |
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The Gem (Orthonama obstipata) is a moth of the family Geometridae. It is a common species of Continental Europe and adjacent lands, though in the northeast, its range does not significantly extend beyond the Baltic region and it is absent from northern Russia. This well-flying species is somewhat prone to vagrancy and able to cross considerable distances of open sea; it can thus be regularly found on the British Isles (though mainly in the south) and even on Iceland.[1]
Under its junior synonyms Nycterosea brunneipennis and Geometra fluviata, the Willow Beauty is the type species of genera Nycterosea and Percnoptilota, respectively. The latter is treated as junior synonym of the former, but Nycterosea, though usually included in Orthonama these days, may warrant recognition as an independent genus after all.[2]
The adult's wingspan is 18–21 mm; in their core range (e.g. Belgium and The Netherlands) they can be seen between April and November, but in outlying regions they may only be regularly encountered in late summer and early autumn, when vagrant individuals abound. This species is strongly sexually dimorphic: males are light brown with a wavy pattern of whitish lines and a broad darker band running across the wings, forming concentric semicircles when the moth is at rest. There is a small whitish-rimmed black spot within the darker band between the center and the leading edge of each forewing. The females are slightly larger and much darker, almost uniformly blackish-brown with an indistinct lighter pattern and a forewing spot like the males have.[3]
The caterpillar larvae feed on a wide range of low-growing core eudicots, but prefer asterids. Host plants recorded from the Central European part of its range include:[4]
Basal core eudicots
The widespread, strongly sexually dimorphic and somewhat phenotypically variable Willow Beauty has been described anews times and again by various authors, even as late as the early 20th century. But all these supposeddly distinct taxa are nowadays considered to refer to a single species. Junior synonyms of the Willow Beauty include:[5]
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