Monday, August 1, 2011

Silver-washed Fritillary

I hadn't anticipated the sheer visual impact of masses of Silver-washed Fritillaries nectaring on masses of dusky purple Pyrenean Eryngo.

A Silver-washed Fritillary, Argynnis paphia, joins a Five-spot Burnet Moth to nectar on Pyrenean Eryngo, Eryngium bourgatii.
(All photos by Narca)

I came home wanting to learn more!

The distinctive silver wash is on the underside of the greenish hind wing, an area that is spotted in most fritillaries. The four stripes on the top forewing of the males are actually androconial scales, or scent glands, used to produce pheromones that females in theory find irresistible. Their courtship flight is spectacular: the female flies in a straight line, while the male performs loop-the-loops around her, showering her in scented scales.

A male Silver-washed Fritillary nectars on Spiny Thistle 
(Carduus acanthoides).
Just one more photo...

Among the largest of European butterflies, these woodland fritillaries are unusual in that the female does not lay her eggs on the larval host plant––various species of violet––but instead places them in crevices in the bark of a nearby tree, usually an old oak. Caterpillar hatchlings consume their egg cases, then spin a silk pad on the tree, attach themselves to it, and go straight into hibernation, deferring their feeding until spring.

With warm March weather, the caterpillars emerge from their crevices and find violets to feed on. When the caterpillar matures it creates a chrysalis, and emerges as an adult about 3 weeks later, in early summer. Their flight period is June through August.

Okay, just one more...

We encountered Silver-washed Fritillaries in good numbers throughout the mountains, both in the Pyrenees and the Guadarramas. Apparently they were in decline in several European countries for a couple of decades, but have been making a comeback in the past 10 to 20 years. Being a powerful flyer, this fritillary is well able to recolonize locales when they again support suitable habitat.

This big, graceful, strong-flying butterfly occurs from Sweden to North Africa, and from Ireland to China and Japan––a classic Palearctic range.

This research has had an added benefit: it solved the identity of another fritillary among the photos––the female Silver-washed Fritillary!

Female Silver-washed Fritillaries lack the striped sex brands on the forewing and aren't as bright an orange.

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