ZEBRA LONGWING BUTTERFLIES
ON A COLD MORNING
Over the long New Year weekend I camped in the
mountains just outside Jalpan. Yet another norther was moving through so the first hours
of 2007 found me in a cold, wet tent. I'd prepared for it, however, and at dawn on New
Year's Day it was cozy lying in my sleeping bag gazing into the misty valley below. Green
Jays orbited around the tent giving me the eye, squawking and flashing their yellow
undertails.
 The drizzle ended and I went snooping. Often on such chilly days you can
find critters who on a warmer day would be moving too fast to get a good look at. That was
exactly the case with the three Zebra Longwing Butterflies, HELICONIUS CHARITONIUS, I
found clinging upside-down beneath a gray, epiphytic bromeliad, as shown at the right.
I've been hoping to get a good picture of this species because they're common here, and
very dissimilar to most butterflies up north because their wings are so long and slender.
When these butterflies fly, their movement seems more buoyant, more fluttery, than that of
our broader- winged species. When I see a Heliconius with its tiptoeing-like
flight sailing along before a wall of lush, dark-green vegetation I really get that
tropical feeling. In fact, the whole genus Heliconius is mainly a tropical one,
with about 40 species.
Evolutionists have paid the genus special attention because an uncommon number of its
species have "converged," in evolutionary terms. In other words, two different
species, both distasteful to predators, over time came to look very similar to one
another. This helped predators learn to avoid their particular color and pattern
combinations. From the predator's perspective it was "one appearance to avoid"
instead of "two appearances to avoid," so each member of the converged pair of
species benefited from the predator's greater ease in avoiding them. This special form of
convergent evolution is referred to as Mullerian mimicry. There's a chart showing several
such converged species pairs at http://www.mun.ca/biology/scarr/Mimicry_in_Heliconius.gif.
Other kinds of mimicry-resulting evolutionary processes -- Batesian, Wasmannian and
Peckhamian -- are described at http://www.geocities.com/brisbane_insects/Mimicry.htm.
The Zebra Longwing isn't a member of any such converged- species pair. One ecological
curiosity about it, however, is that although its caterpillar form seems able to survive
in the forest, the adult form can't compete with other forest species, and is thus fairly
restricted to disturbed sites. It's a weedy-area specialist. Though sometimes thought of
in the US as a Passionvine Butterfly, here its main host plants are Lantana, Hamelia
and Stachytarpheta. The species' distribution extends from deep in South America
through Central America, Mexico and the West Indies into the southernmost US. |
