Saturday, December 13, 2014

Admirals of Winter

Red admiral - Wikimedia
A recent article in the News-Leader described the adventurous life of the red admiral (Vanessa atalanta).  It serves as a reminder of many ways butterflies, these seemingly delicate creatures, survive the winter.  Many of our common butterfly species overwinter as eggs, larvae (caterpillars) or pupae (chrysalis).

The red admiral will migrate north in the spring but not all migrate back south.  Some will hang around, taking their chances on surviving a mild winter.  Like the mourning cloaks and other species living over winter as adults, they don't depend on nectar for their food source.  Instead they primarily consume tree sap, rotting fruit, carrion and animal dung.  They commonly land on humans, presumably attracted to sweat - if one lands on you try not to think about what it ate last.

Dorsal view - Wikimedia
A few other species* such as goat weed leaf wings and mourning cloaks always tough it out as adults, hiding under the bark of trees or other shelters, emerging on rare warm days to stretch their wings and grab a bite before hiding again.  They tend to have drab ventral wing surfaces which blend with the tree bark while resting.  While the red admiral dorsal wing surface is vividly colored, when the wings are folded up, the under wings provide good camouflage.

Camouflaged red admiral Vanessa atalanta roosting on larch trunk © Adrian Hoskins
Some butterfly species migrate as cold weather comes on and their food sources dwindle.  The monarch butterflies famously have several broods as they move north, the last hatch returning all the way to Mexico.  Other migrating butterfly species travel shorter distances, heading north a few hundred miles in the warm months, then returning to the mild weather of the southern states in late fall.  In England, in addition to migrating, there is evidence that the red admiral can occasionally lay eggs in the autumn with adults emerging in the spring.

Yes, England!  They are found in temperate Europe, Asia, and North Africa.  The British love their butterflies and are particularly fond of red admirals.  Some of their population migrates from Southern Europe while recent studies have shown that some survive the winter as adults in southern England.  Southern European residents will migrate to Scandinavia while some North African butterflies will cross to Southern Europe.

Green eggs laid on spiky nettle leaf rather than ham.  Wikimedia
Leaf-wrapped chrysalis -Wikimedia
Eggs are generally laid on nettle leaves in the spring, with a second batch in late summer.  The caterpillars roll leaves around their body as protection until they eat their shelter and move on and wrap up in another leaf.  The hairs of stinging nettles probably provide protection from some predators.  Unlike most leaf rolling larvae which tend to pupate on the ground, the red admiral pupates within the rolled up leaf.

* Missouri species that overwinter as adults include the American lady, anglewings (commas and question marks), goat weed leaf wing and mourning cloaks.

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