The animal kingdom is a wide and varied world, and Mother Nature has come up with some surprising ways to accomplish a variety of feats. Bats "see" with their ears, snakes "smell" with their tongue, and perhaps most strangely of all, butterflies "taste" with their feet. Although some of a butterfly's taste receptors are located on their tube-shaped mouthparts and antennae, most are found on their tarsus, or the bottom segment of their legs. The location of these receptors may seem odd, but they're vital to a butterfly's survival.
Before a butterfly transforms into an adult, it spends its early days as a caterpillar gorging on surrounding plant material and growing, in some cases, around 1,000 times its birth weight. Some caterpillars can munch on a family of plants; the black swallowtail (Papilio polyxenes), for example, is also known as the "parsley worm" because it will eat several plants related to parsley, such as carrots, celery, and parsnips. However, the caterpillar of an endangered monarch butterfly (Danaus plexippus) only eats milkweed. Whether a "generalist" or a "specialist" eater, a butterfly uses its feet to analyze a leaf's chemicals, a process called "contact chemoreception." The chemoreceptors are especially important in allowing female butterflies to "taste" if a plant is safe for her larvae, who will start eating it shortly after hatching. The process isn't perfect, however. In the monarch butterfly's case, it can sometimes be tricked into laying its eggs on an invasive plant species, such as black swallow-wort, causing the larvae to die within a few days. That's why ongoing conservation efforts focus on both planting native milkweed and eliminating any invasive competitors, to make the world safer for monarchs — and their feet.
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