Type species: Samia cynthia (Drury, 1773).
A genus of about 12 closely related species from the eastern Palaearctic and Oriental regions. One, Samia cynthia, has been introduced into several other parts of the world as subsp. cynthia. [Note: Many authors still regard Samia as consisting of one very variable species.]
HOSTPLANT FAMILIES: Mainly trees of the genus Ailanthus (Simaroubaceae), although some species prefer other hosts.
Type locality: China.
Holarctic; eastern Palaearctic region. Pleistocene refuge: Monocentric -- Sinopacific refuge.
Wingspan 113--125mm. Cannot be confused with any other European saturniid, resembling most closely the genera Callosamia (North America), Epiphora (Africa) and Attacus (South East Asia). Body small (<25mm) in relation to wingspan. Male forewings more falcate than in the plumper female, otherwise the sexes are identical, including the 'snake-head' pattern to the forewing tip. The eyespots on each wing are not round but squashed into large crescents. Somewhat variable, with f. advena Watson, 1912 having a reduced grey post-apical area, and f. parisiensis Clément, 1899 with yellowish-brown ground colour.
Although originally from the open lowland forests of eastern and central China, in Europe this nocturnal, or even crepuscular, species is associated mainly with cities and suburban areas, where its introduced host tree is grown as an ornamental or has become feral. It is rarely found above 400m altitude.
Most adults emerge in the late morning, with females calling that same night, or even during late afternoon. Pairing usually takes place just after sunset and lasts for up to 12 hours. Thereafter the female deposits up to 400 eggs on the underside of the hostplants' leaves. By day the adults rest among foliage.
A sedentary, non-dispersive species, with females very attached to the tree or thicket of saplings where they emerged. Most eggs will be laid within this location. Males are more adventurous and will fly some distance in search of females.
In northern Europe during May and June as one generation. In southern Europe a partial second generation may occur in September.
OVUM: Oblong, 1.5 x 1mm, greyish-white with brown gum. Laid in quite large, crescent-shaped batches on the twigs and underside of leaves, usually hatching 10 to 20 days later.
LARVA: Full-fed 65--80mm. Monomorphic.
The newly-hatched, 4mm long larvae consume part of their eggshells. At this stage they are mainly yellow with black-tipped, conical tubercles, black legs, and a black head which is carried almost horizontal. The body bears longitudinal rows of black spots. In the second instar the body colour becomes paler, with the cervical shield reduced to a pair of black stripes. In the third instar the head becomes retractible, the body pale yellow, the dorsal and dorso-lateral tubercles white. These tubercles loose their black tips but little black areas appear on the anal claspers and flap. By the fourth instar the head has become pale brown, the yellowish-green body becomes covered with a white, powdery bloom, and the legs turn chrome yellow. In the final instar some of the body ridges become bluish and the head greenish. Under the powdery bloom, the body is a pale bluish-green.
Newly emerged larvae quickly settle down under a leaf in groups, where feeding usually consists of eating channels into a leaf. Only in the third or fourth instar do they become solitary.
Hostplants. Almost exclusively on the introduced Chinese Tree of Heaven (Ailanthus altissima (Mill.) Swingle), which is grown as a city ornamental and which has also established itself in many parts of central and southern Europe. Larvae have also been found on Forsythia, ashes (Fraxinus), common walnut (Juglans regia), golden rain (Laburnum anagyroides), sweet bay (Laurus nobilis), privets (Ligustrum), Magnolia, Prunus, castor-oil plant (Ricinus), elders (Sambucus), whitebeams (Sorbus), lilacs (Syringa) and many other deciduous trees and shrubs.
PUPA: 27--30mm. Cylindrical, but tapering towards both ends. Pale brown. Formed in a coarse, elongate, pear-shaped, double, unsealed dirty-brown cocoon, which is wrapped in a leaf and attached to the nearest twig by a silken peduncle. These hang from the plant all winter. The overwintering stage. A source of 'wild' silk in its native China.
Tachinidae: Exorista larvarum (Linnaeus), Exorista sorbillans (Wiedemann), Pales pavida (Meigen), Pales pumicata (Meigen); Eupelmidae: Anastatus bifasciatus Fourcroy.
An introduced species found in towns and valleys where Ailanthus trees have become established, such as Paris, the Oise and Gironde (France), Alsace (France), southern Switzerland, northern Italy (Garda, Bagnacavallo etc.), central Italy (Cattolica, Fiorenzuola di Focara, Pesaro, Fano (Lionello Gabucci, pers. comm. 2012)), northeastern Austria and Vienna, Hungary, the Istrian Peninsula (Croatia), and central Slovenia. The population originally introduced into northeastern Spain (Barcelona) has now died out.
An isolated population is also present in the western Republic of Georgia (Zolotuhin, Didmanidze & Petrov, 2011).
Subsp. ricini (Boisduval, 1854) appears to have been released in several areas of Europe and appears to have become established in some.
Extra-limital range. This subspecies is endemic to the Russian Far East, northeastern China as far south as Zhejiang, and Japan; however, it has also been introduced into the eastern USA.
Two, namely ricini (Boisduval, 1854) and pryeri (Butler, 1878); however, some taxonomists regard these as distinct species.