Type species: Saturnia isabellae Graëlls, 1849.
A western Palaearctic genus comprising a single, relict species which is closely related to the genera Actias from North America and eastern Asia, and Argema from eastern Africa.
HOSTPLANT FAMILIES: Pinaceae, particularly members of the genus Pinus.
(Taxonomic note. A in-depth cladistic analysis of the Actias/Argema/Graellsia species group by Ylla, Peigler & Kawahara (2005) demonstrated that Graellsia should be retained as a genus separate from Actias. It appears to be the most basal of this group, being the first species to split off the Actias/Argema evolutionary line.)
Type locality: Spain, Madrid Province, Sierra de Guadarrama, Monte de Pinares Llanos.
Holarctic; western Palaearctic region. Pleistocene refuge: Monocentric -- Atlantomediterranean subsection of the Mediterranean refuge. (Apparently a relict from the Tertiary Period, whose nearest relatives are to be found in eastern Asia.)
Wingspan 65--100mm; bred individuals can be considerably smaller. A pale green species similar in shape and size to the North American Actias luna, but differing in having the wing veins heavily outlined with reddish-brown scales and with yellow replacing the pale green on the hindwing tails and wing submarginal areas. The broad, outwardly curved tails are more than twice as long in males than in the females.
This nocturnal species inhabits mature pine forests at altitudes of 500--1800m, particularly those subject to seasonal low-level cloud cover (i.e. fogs) when the moths are on the wing. Although tolerant of large variations in humidity and temperature, this species cannot tolerate extreme heat or prolonged drought. Both sexes become active at dusk, even at temperatures as low as 5°C. Pairing rarely lasts longer than two hours.
This species prefers to rest near to the forest floor on the stems of saplings and on small branches which, particularly in the male, it 'clasps' with its wings. In this position it is remarkably well camouflaged.
In Canton Valais, Switzerland, it occurs in light pine forest on steep, south-facing slopes at between 800 and 1600m altitude (Heinz Rothacher, pers. comm. 2005).
Depending on latitude and altitude, March to the beginning of July as a single generation.
OVUM: Oval, 2 x 1.8mm, but tapering dorsally. Off-white with dark olive-green speckling. A prominent micropyle is evident. Laid singly or in small groups at the base of young pine needles, usually hatching 10 to 15 days later.
LARVA: Full-fed 70--80mm. Monomorphic.
The newly-hatched, 5mm long larva consumes part of its eggshell. For the first three instars it is mainly greyish-brown with irregular markings and humps, resembling the twigs on which it rests. In most larvae the fourth instar resembles in shape that of Actias selene, but the basic body colour is greyish-brown with some pine-green, brown and yellow irregular blotches: the cervical shield bears four spines. The fifth instar larva is basically apple-green with a broad brown dorsal band edged with white. Each segment has an encircling band of dull red broken by 2-3 white dashes. The thoracic segments are also ringed with yellow, and the ventral surface is reddish-brown, as is the head. Fine white dots cover the entire body, from which a few long brown hairs arise.
Under optimal conditions many larvae will complete their development in four instars, with the final colour pattern appearing in the fourth.
Initially, small larvae rest on pine needles. From the second instar onwards, however, most tend to rest head down at the base of a needle or on an exposed older twig, where they are remarkably well camouflaged. Up until the fourth instar nearly all prefer to eat older needles from the previous year.
The full-grown larva is solitary and often rests with the anterior segments puffed up so as to resemble a pine-cone. In the cool conditions of its habitat it can take up to two months to mature, eating copious quantities of needles in the process. At this stage newer needles may be consumed, as long as they have matured a little.
Hostplants. Confined to species of Pinus, such as Scots pine (P. sylvestris) and the various subspecies of black pine (P. nigra); however, in captivity many larvae will accept Liquidambar as an alternative host.
PUPA: 32--35mm. Mid mahogany brown and similar in shape to that of Saturnia pyri. Formed in a thin-walled, 55 x 30mm, irregular to oblong, single, unsealed, golden-brown, tapered cocoon, which incorporates dead pine needles. These are preferentially spun at the base of the hostplant, either within the needle mat or at the soil/mat interface. Most are orientated horizontally, with the trapdoor through which the moth will emerge situated off-centre on the dorsal surface of the thicker end. Very cold-tolerant, and may overwinter more than one year if the winters are not cold enough.
Tachinidae: Compsilura concinnata (Meigen), Drino inconspicua (Meigen), Masicera silvatica (Fallén), Phaonia signata Meigen; Ichneumonidae: ?Pimpla robusta Rondoni, ?Ichneumon microstictus Wsm., ?Ichneumon sulfuripes Rondoni.
The mountains of central Spain, such as the Sierra de Guadarrama near Madrid, the Montes Universales near Teruel, as well as the Sierra de Javalambre and Sierra Gudar. Also southern Spain in the Sierra de Segura (Province Jaen). It is common in the central and eastern Pyrenees of northern Spain, in the Valle del Roncal (Province Navarra) and Sierra de Montgrony (Province Gerona). From here it extends north a little, into southern France.
It is also found in a small area of the High Alps in southwestern France around Briancon, as well as Canton Valais, Switzerland. It has become well established in the latter since it was first observed/introduced there in 1987 (Heinz Rothacher, pers. comm. 2005). (It has also been reported recently from northern Italy, but this remains unconfirmed.)
[This cold-adapted species may have once had a much greater range during the last inter-glacial period. At the end of the last ice-age, when Europe warmed rapidly, Graellsia isabellae probably got 'stuck' in cool, southern, montane refugia and was thus unable to re-colonize its former more northern range.]
Extra-limital range. None.