High in the canopy of a Latin American rainforest, a bright yellow, orange, and black butterfly flutters along. It is a Heliconid butterfly, looking fora passion flower vine to lay her eggs on.
She is one soldier in a war for survival between Heliconid butterflies and passion flower vines. For the butterflies, the goal is to lay their eggs; for the vines, to keep from being eaten.
When the eggs hatch, the Heliconid caterpillars will feed on the vine’s leaves. Most insects can’t do this, because passion flower vines are poisonous.
Poison as protection
Heliconid caterpillars can eat these leaves safely. In fact, for them, the poison is an advantage: it stays in the caterpillars, making them poisonous…so birds that would otherwise eat them leave them alone.
And when these Heliconid caterpillars grow up and turn into butterflies, the chemicals still remain. Heliconid butterflies too are poisonous.
Sometimes, passion flower vines start producing a new poison that works even on Heliconids…but in a while, news types of Heliconids develop that are immune to the news poison. The struggle for survival between plants and plant-eaters goes on and on.
Advertising and false advertising
Of course, being poisonous is no protection unless animals that might eat you know you’re poisonous…so a Heliconid butterfly advertises. It wears bright colors that are easy to recognize.
Like a security alarm sticker on a house, the Heliconid’s coloring gives a warning: <<Don’t mess with me. I am dangerous!>>
Other kinds of poisonous butterflies imitate the way the Heliconids look, to show that they too are dangerous to eat.
But imitation goes further. Butterflies don’t own copyrights on their colors…so some butterflies that are not poisonous also look like Heliconids. They are trying to tric predators into leaving them alon – by pretending they are dangerous to eat.
Caterpillars, keep off!
In this war, the passion flower vines fight back. Poison is just the beginning. Here are some other means that passion flower vines use to get rid of Heliconid caterpillars.
disguises – Some passion flower vines produce leaves that look like the leaves of other kinds of plants. If the butterflies think they aren’t passion flower vines, they won’t try to lay their eggs here.
guards – On occasion, passion flower vines get ants to guard them. The vines supply a special nectar that the ants like to eat. In exchange, the ants pick off any young Heliconids that develop on the vines’ leaves.
fake eggs – A passion flower may grow imitation eggs. When the butterfly comes to lay her eggs, she thinks that the leaf is already occupied…and goes off to look for an empty vine.
weapons – Some passion flower species grow hooked hairs on the surface of their leaves. These hairs kill the caterpillars.
dumpers – Since Heliconids like to lay their eggs on the tendrils of the vine, some vines grow special extra weak tendrils. When an egg laid on one begins to develop and becomes heavier, the dumper tendril can’t hold its weight anymore, and the egg falls off.