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scientific name    Aglais milberti    

common name     Milbert's Tortoiseshell

Found in many habitats, from prairie coulees to boreal forests and mountain tops.

One, or possibly two generations per year, usually found in early spring and again in late summer.

The solid black wing bases edged with bright yellow and orange are unmistakable. Our populations are the nominate subspecies. Recent work by Nylin et al. (2001) shows that Milbert's Tortoiseshell is more appropriately placed in the genus Aglais.

life history
The conical eggs are green with eight or nine vertical ridges (Guppy & Shepard 2001). Small larvae live communally in silken nests on the hostplant. Mature larvae are solitary, and are black with yellowish subdorsal lines, finely dotted with white, and bear branched spines (Layberry et al. 1998). This tortoiseshell is encountered much more regularly than other tortoiseshells in Alberta, apparently since it does not experience the large fluctuations in number that occur in the California and Compton Tortoiseshells. Adults are strong, rapid fliers but are easily approached when nectaring at flowers. Milbert's, like its other close relatives, overwinters as an adult, emerging early in the spring with faded and often tattered wings. The offspring of the hibernators appear from July onward. Bird et al (1995) state that there are two generations annually, but this needs confirmation; multiple generations in Canada are known only from southeastern Ontario (Layberry et al. 1998).

Not of concern.

diet info
The larvae feed on stinging nettle (Urtica dioica) in British Columbia (Guppy & Shepard 2001) and in Alberta (D. Lawrie, unpubl. data). Unlike other members of the 'hibernator' group, adults of this species are avid flower visitors, but will also visit tree sap or rotting fruit.

Alaska south to California and New Mexico, east to New England and Newfoundland (Layberry et al. 1998, Opler 1999).

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Comments (2)Add New Comment

Joe Belicek (2013-09-10)
Tilden, (1976), found no instance of true diapause in the adults of Lepidoptera. If so-called hibernating individuals of Nymphalis antiopa are brought into a warm room, they return to activity in a short time. If placed in a refrigerator, they soon become inactive again. Such individuals can be alternately chilled and warmed a number of times without apparent injury.

joe Belicek (2014-03-06)
Aglais milberti (Godart, 1819)

The Anglewing, Aglais milberti is the sole representative of the genus Aglais on the North American continent. Seven other species inhabit the Old World (A. caschmirensis, A. connexa, A. ichnusa, A. ladakensis, A. nixa, A. rizana, A. urticae). The larval food plants for all Aglais species are nettles (Urtica spp.) The reports of other food plants like Elms, Willows etc., for Aglais milberti are at present unconfirmed and probably erroneous since the larva needs to construct a shelter from the leaf, in shape & texture specific to nettles. In stature, the butterflies of the genus Aglais are similar to Polygonia but mucj smaller than Nymphalis or Roddia. The wingspan averaging 41 mm, hence their common name Small Tortoiseshells. Dorsally, the ground colour is (without exception) in all three mentioned genera is orange-brown. As a rule, all species of Anglewing butterflies are cold hardy and survive the winter as adults in hibernation. The adaptations that enables these butterflies to stay alive and not to freeze in subzero temperatures is simple. The body fluids are fortified with antifreeze (alcohols & glycerols) acquired in the fall by feeding on fermenting organic materials (i. e. fallen fruits). In Alberta, this species is the most abundant & widely distributed Anglewing, found throughout the Province. Known for its rapid flight, the folklore of the Blackfoot Indians has it, that to prove their agility, the grooms-to-be were required to catch Milbert's Tortoiseshell butterflies and bring them to the Chief before the marriage could be arranged (Ted Pike, pers. comm.). On the Prairies this species is not common. In the genus Aglais, the female lays the eggs in a large batch on the undersurface of terminal shoots of nettles. The batch or cluster, typically includes upwards of 100 eggs (the largest batch of 713 eggs was reported by Scott, (1989). Only the plants with a sunny exposure seem to be selected. Initially, the eggs are leafy green, with 9-10 longitudinal ribs or keels. After hatching, the young larvae ascend together to the top of the leaf and spin a silken web nest. The young larvae live gregariously in the web of a nest until the third molting, when the larvae tend to break-up into smaller groups. The tight, gregarious mode of life affords some ?collective protection? for the group, mainly against parasitic wasps. When alarmed, the gregarious larvae of the whole brood stir in unison in a convulsive way. However, this behaviour is effective only at the beginning of the attack. In the laster instars, the larvae are solitary, but hiding during the day in a rolled-up nettle leaf. The ?tubular leaf tent? is formed by tying together the sides of the leaf with silken strands. At first, the larva eats through the main ribs at the base of the leaf, then ties the flaps together, forming an open-ended tube. On nettles also feed larvae two other species, i. e. Polygonia satyrus and Vanessa atalanta. The tents constructed by larvae of Vanessa atalanta are similar to those of A. milberti. The leaf ribs are cut at the base, rolled together in such fashion that the underside surface of the leaf is on the outside. Zin contast, the larva of Polygonia satyrus undercuts the whole petiole at the base and then ties the drooping leaf with silk so that the dorsal surface is on the outside. The larvae of all three species leave the leaf tent shelter to feed at night outside it. The last instar larvae The fully grown larvae of A. milberti leave the nettles and pupate some distance away, usually on foliage & twigs of nearby plants. In Alberta, typically two generations are produced per year. For British Columbia, Guppy & Shepard (2001) report only one generation. This is exceptional for this species. Elsewhere in North America, up to three generations were observed, like in the European A. urticae. In Alberta, only the adult butterflies survive the winter in hibernation. However, according to the literature, in some areas elsewhere also the pupae overwinter as well.

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Specimen Info
There are 105 specimens of this species in the online database
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Specimen List (105)


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