As a child, I was attracted to butterflies by their color and patterns: sometimes subtle, sometimes vibrant, sometimes simple and sometimes intricate. As I took a closer look, I sometimes noticed that the trailing end of their wings had a piece missing, as though something had taken a bite out of it.
I wasn’t the first person to observe this. Since the time of Darwin, biologists have described butterfly coloration and patterns as defense mechanisms that evolved in response to predation by birds. There are two major categories of defense mechanisms: aposematic coloration and mimicry.
Aposematic coloration are warning signals that consist of bright or contrasting colors. These signals send a message: don’t even think of eating me! For example, Monarch butterfly caterpillars eat milkweed leaves, which contain bitter-tasting plant toxins. “These toxins stay in the animals when they become adult monarchs…and ”make the butterfly taste bitter”. When a bird takes a bite, “it will typically spit the butterfly out and will avoid them thereafter.”
Mimicry is “the resemblance of one organism to another”. The purpose is “concealment or protection from predators”. The “eyespot” patterns found in some butterflies are an example of this. Large eyespots are thought to “deter bird predators through intimidation”, since large eyes indicate a large (and possibly hungry) animal. But smaller eyespots also work by misdirecting birds away from the head, especially when the eyespot is combined with antennae-like projections at the trailing edge of the wing. This is sometimes known as the “false head hypothesis”.
In both examples of butterfly defense mechanisms, the predators were assumed to be birds. But now, in a new study, scientists have expanded that list of predators to include jumping spiders!
Dr. A. Sourakov, a biologist at the University of Florida, studied the butterfly-hunting behavior of jumping spiders (Phidippus pulcherrimus). These jumping spiders were very precise, attacking the head region and delivering “venom to the vital center to instantly paralyze the prey.”
But when the butterfly wings had a “false head” (eyespot and tails that look like an antennae), such as found on hairstreak butterflies, the attack failed. Accorded to Dr. Sourakov, the “hairstreaks constantly move(d) the hind wings” and “the spider always attacked the butterfly’s false head, thereby avoiding its vital organs.”
The more I learn about butterflies, the more I realize they’re more than just a pretty face. They’re athletes too – and capable of an epic spider fake out!
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Trail Maintenance Schedule. Come join our volunteers as they help maintain our trails. Contact Steve at email@example.com for time and place.
Wednesday mornings, May 1, 8, 15, 22 & 29.
Saturday mornings, May 4 & 18.
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As the days grow longer, migrating birds become more active, changing locations. Learn about some of the birds that live and pass through our local mountains. Beginners are welcome. Binoculars optional. Meet at Towsley Canyon’s front parking lot. For more information go online.
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Source: Santa Clarita News