Katydids don't sing with their breath, vocal cords and mouth as we do. They sing with their wings. That may sound like bad freshman poetry, but it's the literal truth. At the front of each upper wing, a katydid has a flat, triangular area embossed with ridges. When rubbed against each other, the ridges of the two wings produce a series of rapid scratches. Amplified by the echo chamber formed by the tent of the wings behind the "instrument," the sound becomes louder. The true katydids of the treetops (genus Pterophylla) are the loudest of all. Each species of katydid has a different song, and some are more easily identified acoustically than visually.
The wings of katydids serve two other functions - flight and camouflage. Concealed beneath the upper, sound-producing pair of wings are the flight wings. Normally folded in origami fashion and tucked under the upper wings, the semi-transparent flight wings are extended when a katydid leaps into the air, propelled by rear jumping legs longer than a grasshopper's. Most katydids can't fly far, but a short glide from bush to bush or limb to limb can be a life saver.
As camouflage the stiff upper wings serve ably. Shaped and colored like leaves, blades of grass, stems and other parts of plants, the forewings of katydids help to make them all but invisible as they slowly traverse the vegetation where they live. The wobbling walk of a katydid looks unsure and hesitant, even tipsy, but the shaky gait mimics the shivering of a leaf in the breeze. The forewings of some tropical katydids are marked with false leaf blemishes, irregular blotches of yellow and brown, and even transparent patches resembling holes chewed through leaves by caterpillars, beetles, or . . . katydids.
This brings us to a male oblong-winged katydid we found in our back yard this week. His right side was normal, the usual leaf green. But his left side was highly unusual. The left forewing had a pale blotch outlined in dark brown. Just below the blotch a nip had been taken out of the bottom of the wing, and the left hind leg - the jumping leg - was missing. We guessed that this katydid was attacked and injured by a predator, but managed to escape with its life. Its wing was damaged and it lost a leg.
What about the blotch, though? It could be a result of injury, the yellow and brown colors a curious consequence mimicking the mimicry of its tropical relatives. Or was the blotch present at the time of attack, an anomaly of genetics or development, a birthmark of sorts, or an existing scar? This question raises broader ones: Could variants (including mutations) of the genes that control healing and the formation of scar tissue be activated in early development to create scar-like markings that improve the effectiveness of camouflage? Could this be an explanation (perhaps not the only one) for the false holes and blemishes that adorn the wings of many tropical katydids, mantids and other vegetation-dwelling insects? If so, that would go a long way toward understanding and explaining how appearances (and perhaps behaviors) often deemed "miraculous" could come about through everyday evolutionary change.