I approach the migrants for a closer look, knowing full well what they are but still dazzled by the details, by the almost comical earnestness of the charade they embody. The "twig" is a stick insect, a magnificent specimen of the Phasmatodea clan, its outer sheath a persuasive rendering of striated bark, its tubular body and head punctuated by fake axillary buds and leaf scars—the little knobs and notches that make a twig look twiggy.
During the day these insects move little and are nearly impossible to distinguish from the sylvan backdrop they imitate, and that, of course, is the point: to remain invisible to sharp-eyed predators that use vision to hunt. Come nightfall, however, sticks and leaf katydids shake off their vegetal torpor to do some feeding of their own—on leaves and forest-floor detritus—at which point their ancient artifice can be admired by grace of our modern artificial lights.
We are drawn to mimicry and disturbed by it too. As children, we play dress up and let's pretend, and we understand our fellow hominins through private reenactment. Our most elaborate masquerades—for Halloween, say, or the Day of the Dead—are often tangled up with our deepest fears. What self-respecting Hollywood slasher would be seen without his Munchian mask or mother's wig?
Mimicry in nature likewise can charm or repel us, but whatever our human judgments, this much is true: Scamming works, and the natural world abounds with P. T. Barnums, which fill every phyletic niche, sucker every sense. Biologists have barely begun to tally life's feinting legions or trace the evolutionary and genetic details of each imposter's disguise. Sometimes the deception serves as camouflage, allowing its bearer to elude detection by predators, prey, or quite often both: In Panama I found a mantid that looked like a few sprigs of radicchio, the perfect cloaking device for a stealth hunter of leaf-eating insects that is itself much coveted by insectivorous reptiles and birds. At other times the swindler wants its merchandise to be noticed; that's the whole point. An anglerfish wags its head until its fleshy protuberance shimmies like a worm and baits other fish. Carrion orchids sprout large, purplish, fetid blossoms that look and smell like dead meat to attract scavenger flies, which will alight on the flowers, get dusted with pollen, and maybe, just maybe, help the orchid breed.