AGLIA Ochsenheimer, 1810

Aglia Ochsenheimer, 1810, Schmetterlinge Europa 33: 11.

Type species: Phalaena tau Linnaeus, 1758.

A Palaearctic genus comprising three (maybe four) species, of which Aglia tau occurs right across the northern Palaearctic, except for the British Isles and Japan; Aglia homora Jordan, 1911, which has only been recorded from the provinces of Gansu, Shaanxi and Sichuan, China; and Aglia japonica Leech, [1889], which is endemic to Japan.

HOSTPLANT FAMILIES: Many trees and shrubs, but with a preference for the Fagaceae.
 

AGLIA TAU (Linnaeus, 1758) -- TAU EMPEROR

Phalaena Bombyx tau Linnaeus, 1758, Syst. Nat. (Edn 10) 1: 497.

Type locality: [Europe].


BIOGEOGRAPHICAL AFFILIATION

Holarctic; Palaearctic region. Pleistocene refuge: Polycentric.


ADULT DESCRIPTION AND VARIATION

Wingspan 60--84mm. The sexually dimorphic and dichromatic adults are like no other moth from the region, with the larger females (illustrated) being less well marked and less brightly coloured than males, which have less pointed forewings. Although most adults are yellowish-orange, some are heavily dusted with dark-brown or black scales (f. melaina Gross, 1898); the latter are especially common in cooler, mountainous areas. Other forms include f. ferenigra Thierry-Meig, 1884, in which the submarginal areas of all wings are heavily dusted with dark scales; f. cerberus Schultz, 1905, in which the hindwings are black; f. cupreola Werner, 1902, in which the females are copper-red; and f. decolor Schultz, 1905, in which both sexes are pale. There are many more forms in this variable species, too many to be mentioned here. The eyespots have iridescent purple centres.


Male Aglia tau (resting, but alert; underside), Czech Republic. Photo: © Tony Pittaway. Male Aglia tau (alarmed; underside), Czech Republic. Photo: © Tony Pittaway. Female Aglia tau, Czech Republic. Photo: © Tony Pittaway.

ADULT BIOLOGY

Most adults emerge in the early morning, with females calling that same day, often from the base of trees up which they have climbed. Although the females are nocternal, the diurnal males zigzag wildly through open woodland on sunny mornings (9--11h) in search of these, with several often piling up on the same hapless object of their desire. Pairing lasts for only a few hours. After separation, males fly off to rest and usually cease all activity by mid afternoon. Come evening, the female climbs to the highest vantage point possible before launching herself clumsily towards the nearest shadow which, often as not, is a tree. When at rest both sexes generally sit on tree-trunks or the forest floor with their wings closed vertically over the abdomen.

This is a species of deciduous forests up to 1600m altitude, showing a preference for beech (Fagus) woodland.


FLIGHT-TIME

Depending on latitude and altitude, late March to the beginning of June as a single generation, which coincides with the appearance of leaves on the trees.


EARLY STAGES

OVUM: Cylindrical with rounded ends; 2.5 x 1.9mm; usually dark-chestnut but sometimes cream. Laid in rows of up to ten on the branches and trunks of trees, usually hatching 10 to 12 days later.


Eggs of Aglia tau, Czech Republic. Photo: © Tony Pittaway.

LARVA: Full-fed 60mm. Monomorphic.


First instar larva of Aglia tau, Czech Republic. Photo: © Tony Pittaway. Second instar larva of Aglia tau, Czech Republic. Photo: © Tony Pittaway.

The newly-hatched, 5mm long larvae is spectacular. Although the head and body are pale green, two red and yellow bifurcated spiny 'horns' project forward from segment one, with another pair projecting backwards from thoracic segment three. A single horn of the same colour projects up vertically from abdominal segment 7. The body is covered with small yellow tubercles and there is a pronounced subspiracular line of the same colour running from around thoracic segment one to the anal clasper. As the larva grows the 'horns' shrink, disappearing in the final instar, the yellow markings become more intensive, and the segments become sharply humped, giving the body a serrated outline. A single oblique yellow line appears laterally on each abdominal segment, as well as a black-centered red spot on the side of abdominal segment one. This species may go through 4 or 5 instars.


Third instar larva of Aglia tau (feeding), Czech Republic. Photo: © Tony Pittaway. Third instar larva of Aglia tau (resting), Czech Republic. Photo: © Tony Pittaway. Final (fourth) instar larva of Aglia tau, Czech Republic. Photo: © Tony Pittaway.

The larvae are initially gregarious, but rapidly become solitary and sedentary. In the later instars they often rest in a rolled-up leaf between feeding bouts.


Hostplants. Many species of tree and shrubs, with a preference being shown for beech (Fagus sylvatica). Also, oaks (Quercus), hornbeams (Carpinus), birches (Betula), maples (Acer), hazels (Corylus), limes (Tilia), pears (Pyrus), apples (Malus), mountain ash (Sorbus aucuparia), alders (Alnus), hawthorns (Crataegus) and willows/sallows (Salix). In many lowland forests, Tilia and Salix replace beech as the preferred host.

PUPA: 22--27mm. Bullet-shaped, tapering anteriorally. Blackish-brown and rough. Formed in a few strands of silk among litter at the base of a tree. There is no cocoon. The overwintering stage.


Pupa of Aglia tau, Czech Republic. Photo: Mark Boddington. Male pupa of Aglia tau (lateral view), Czech Republic. Photo: © Tony Pittaway.

PARASITOIDS

Tachinidae: Drino lota (Meigen, 1824), Senometopia separata (Róndani, 1859).


DISTRIBUTION

From northern Spain, France and southern Scandinavia across central, northern and eastern Europe to the Ural Mountains (Nupponen & Fibiger, 2002) and western Siberia, with isolated populations in the Apennine Mountains east of Florenz, Italy (Dapporto, Fiorini, Fiumi & Flamigni, 2005), in the Crimea (Ukraine), the Ciscaucasus (Zolotuhin, Didmanidze & Petrov, 2011), and the Alborz Mountains of northern Iran (Nässig, 1981); recorded from as far north as Arkhangelsk Oblast in european Russia (Kozlov, Kullberg & Zverev, 2014). This species is missing from the British Isles and has not been recorded from northern Turkey, nor the Caucasus Mountains.

Extra-limital range. From the Altai Mountains across southern Siberia (Izerskiy, 1999a), Mongolia and southern Yakutia (Kaimuk et al., 2005) to the Russian Far East, northeastern China and North Korea.


OTHER SUBSPECIES

None. The former subsp. microtau Inoue, 1958, is a subspecies of Aglia japonica Leech, [1889], which is endemic to Japan.



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