Art Shapiro's Butterfly Site - Nymphalis

Nymphalis antiopa

admin — Sun, 28 May 2006 18:08:26 +0000

A very distinctive and charismatic butterfly, best known for its conspicuous activity in late winter, flying and acting territorial before any trees have leafed out or any wildflowers are active. It hibernates as an adult. In the Sacramento Valley there appears to be only one brood (in spring); the resulting adults migrate upslope and breed in the mountains. There is a reverse downslope migration by the next generation, in late September-October. It is not obvious why this seasonal altitudinal migration occurs, but both the California and Milbert's Tortoiseshells, its closest relatives, do it too.

The eggs are laid in clusters and the spiny black larvae, marked dorsally with red, feed communally in the open on Willows (many species, including cultivated Weeping Willow, S. babylonica) and occasionally on Hackberry (Celtis) or Elm (Ulmus) in cultivation. The pupae are grayish-violet, finely dotted with black, and tend to be formed as clusters.

There is a very dramatic aberration, named "hygiaea," in which the yellow border expands to obliterate the blue spots and cover the entire outer 40% or so of the wings. It has been taken or seen a few times in our area, most recently in Rancho Cordova in 2006.

In recent years populations of this butterfly have collapsed regionally; it disappeared from West Sacramento for several years and has been very scarce and erratic at other low-altitude sites; there was some improvement in 2005 and numbers of hibernators at low altitude were up in 2006, but very bad weather may have prevented much if any recovery.

Adults are more likely to visit sap, injured fruit, dung or mud than flowers, though spring indivuals often nectar at Willow catkins and autumn ones tank up at Rabbitbrush. In autumn one often sees adults "hanging out" within willow trees in the high country. It is not obvious what they are doing and why. Some adults overwinter even at Donner. They emerge just after snowmelt, which often coincides (late May-June) with when immigrants from the new brood arrive there from downslope!

Nymphalis californica

admin — Sun, 28 May 2006 18:08:25 +0000

Along with the Painted Lady, this is a mass migrant that makes news at irregular intervals by tying up traffic! The "Tortie" overwinters as an adult and can sometimes be seen sunning itself in midwinter on mild days. It is generally common in foothill canyons in late winter, ovipositing on the young, tender growth of various species of Wild Lilac (Ceanothus). The spiny, black-marked-with-yellow larvae feed gregariously, without a web, and in big years can defoliate whole stands of the plants. They often pupate on the bare, leafless stems en masse, the grayish-violet pupae looking like some strange kind of leaf and twitching in unison when disturbed. Adults emerge in late May to early June and almost immediately emigrate, going north or east and upslope. Breeding localities in summer vary widely from year to year - sometimes in the high southern Sierra, sometimes in the Cascades... sometimes only in far northeastern California or even farther north. The migrant females lay on the tender growth of high-altitude Ceanothus such as Tobaccobrush and Snowbrush, which again may be defoliated. Adults emerge in late July and migrate to estivating grounds, generally above tree-line. These are often in the high country of Yosemite, Sequoia and Kings Canyon National Parks, but can even be in the Trinity Alps, South Cascades, or (as in 2005) on Mount Rose! Estivating Torties do little but "hang out," and many high-altitude hikers have described their encounters with millions of them in mystical terms (they often identify them as Monarchs!). In late September these butterflies scatter downslope to hibernate in the foothills--they are the late-winter butterflies of the new year. Estivators-hibernators thus may live 9 or 10 months as adults.

Although the rhythm of seasonal migration is constant, the numbers of individuals vary over several orders of magnitude - but not in an orderly "cycle." Records at Gates Canyon, in the Inner Coast Range, are virtually all of hibernators and their offspring just before emigration; the species is totally absent from July through late September or October. Records on the floor of the Sacramento Valley are of migrants away from the Coast Range (May-June) or back to it (late September-early October). Very rarely an individual may overwinter on the Valley floor and reappear near its wintering site on fine days. Some individuals do hibernate at higher altitudes, and show up right after snowmelt - but this frequently coincides with the arrival of masses of upslope migrants in June.

Occasionally the upslope movement encounters the retreating snowline, forcing females to lay only on Ceanothus that have melted out. This can result in enormous larval densities, total defoliation of the hosts and mass starvation -- while close at hand, plants that were still under snow when the eggs were laid sit absolutely untouched!

Adults visit flowers of many kinds, aphid and scale honeydew, damaged fruit, sap--and mud: a mud puddle in a mass migration of Torties is a memorable sight, often with hundreds or thousands packed side-by-side on the damp surface.

Sexual dimorphism is minimal, and remarkably little variation occurs in the wild although (as is usual for Nymphalini) bizarre aberrations can be induced by cold-shocking the pupae in the lab.

The California Tortoiseshell is closely related to two Old World species which, unlike it, are rare and in serious decline.

Nymphalis milberti

admin — Sun, 28 May 2006 18:08:24 +0000

Recorded from most sites on the transect, but this is an altitudinal migrant that spends the winter as an adult near sea level, breeds there in spring, then shifts to the Sierra (particularly the East slope) for summer breeding before returning west in autumn. Fresh adults are often common on Coyotemint at tree-line on Castle Peak, even though there are no host plants that high. They were apparently born and bred on stinging nettle (Urtica holosericea) around Truckee and Loyalton! As a riparian plant, nettle should be available all summer at low elevation so it is unclear why this species undergoes its annual trek up and down the Sierra Nevada - but it does. Larval colonies have been found on the Sacramento Valley floor in places where adults have never been seen; it has been found breeding in West Sacramento and North Sacramento and occasionally uses the small introduced nettle, Urtica urens, as well as the large native species. The eggs are laid in masses, and the black-and-yellow spiny larvae are colonial and quite conspicuous.

Adults are most likely to be recorded near sea level in late winter, less often in autumn. In the Sierra they can be seen from May to September. There are probably two generations a year, possibly three. In addition to Coyotemint they are partial to Rabbitbrush and, oddly, they often visit flowers of Bitter Cherry and Choke Cherry, not usually visited by butterflies. There is no significant variation.