PASSION FLOWER AND ITS ASSOCIATED BUTTERFLIES

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If you search along the weedy margins of the railroad track you cross just before you enter the refuge, any time between May and August, you'll probably find one of the most interesting flowering plants and plant-herbivore systems in the southeast, Passiflora incarnata, commonly called maypops or simply passion vine.  They also occur along the margins of the dikes in some areas, especially along the east side of Pool 1.

Passion vines produce beautiful, large flowers that are easy to find once they open. These large, complex flowers open quickly at about 11 a.m., and last only one afternoon before shriveling and setting fruit.

Passion vine is chemically protected by cyanogenic glycosides, which prevent most plant-eating insects from feeding on it.   It is, however, fed upon by the larvae of two specialized butterflies, which feed on no other plants.

This is Agraulis vanillae, the gulf fritillary.  These butterflies are often present in large numbers, especially from mid-late summer.  Adults can usually be found in the vicinity of passion vines, and the plants themselves often have several larvae per plant.  Gulf fritillary caterpillars are more often found on passion vines in open, full sun, and are usually found feeding on older leaves away from the tip of the vine.

These are the eggs and larva of the zebra longwing, Heliconius charitonius. These butterflies lay their eggs in clusters at the very tip of the growing vine, and are more often found on plants that are at least partially shaded.  Thus, the two species of butterflies seem to avoid direct competition by feeding on different parts of the plants, and selecting different microhabitats.

Reproductive behaviors of adult Heliconius are amazing.  An hour or two before female butterflies eclose (emerge) from their pupae, they release pheromones to attract males. Males attempt to monopolize the pupa by jostling with each other (left)  until all but one of the males is driven off.  The victor hangs around to await the emergence of the female.   Nothing too unusual, right?

As it turns out, this randy little bugger can't wait.  He somehow penetrates the exoskeleton of her pupa with the tip of his abdomen before she even emerges.  They   begin mating while she is still inside.  As she emerges from her pupa, and begins to unfold and dry her wings (right), the pair is already in copula.  This behavior is uncharitably called "pupal rape".

The butterflies and caterpillars are relatively easily found when they're present, which is usually for most of the summer and early fall.  The reproductive behaviors of Heliconius will be tougher to observe; the females seem to normally emerge early in the morning, so if you're in the vicinity of passion vines where Heliconius caterpillars can be found, look on surrounding vegetation for pupae.  The combative jostling of a couple of males around a little brown lump is a sure sign that these cool behaviors are about to begin.

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