Naturespeak A naturalist's view of the world

August 15, 2008

The Quiet Start to a Noisy Day

Filed under: Uncategorized — wykes @ 5:25 pm

The emergence of the Dog Day Cicadas in late summer is not a subtle affair. The event is heralded from the tree tops with a flurry of dry rattling trumpet blasts issuing from the adult insects. If you are out and about during the day or early evening, youll hear the extremely loud calls of these insects and probably not even think about it. They are as much a part of the summer soundscape as the cricket chorus and the distant drone of lawnmowers. Also known as Dog Day Flies, Harvest Flies, and incorrectly as Locusts, the cicadas number among the loudest insects on earth. The Australian version, called the Green Grocer, is purported to be THE loudest insect on earth, as a matter of fact. Back here in the states, this auditory treat is THE sound of summer (Dog Day Cicada Call).

Witnessing the soft start to this loud life can be a fascinating part of the visual landscape as well. Annual cicada nymphs emerge out of the ground every year. Unlike their 17 year counterparts, individual D.D.Cs spend 2-7 years mutely tunneling through the dark soil and feeding on root sap. When the Dog Star is high in the summer sky, mature nymphs feel the call to leave the underworld.

Their impulse is to put some vertical distance between themselves and their childhood home and they climb anywhere from a few inches to 10 feet up the side of a tree. Nymphs are equipped with powerful forelimbs complete with opposable grips and lamellae (teeth) in order to scale the bark (see here). Internally they are already changing into flighted beasts and their movements are slow and deliberate due to their loosening skin and shifting musculature.

At some point, comfortable with their altitude, they hook firmly into the bark substrate and prepare for the inevitable. Body fluids are slowly pumped into the thorax in order to build up pressure in that region. Around about noon, the dramatic shift from nymph to adult begins as the old skin splits under the pressure. The newly formed cicada pushes out from its old casing and hangs backward at a seemingly uncomfortable angle. New legs are pulled out of the old and the folded wings are pulled out of their pockets.

While in this precarious state (see here) the insect pauses and begins to un-furl its wings. When viewed head on, the wonderful symmetry of the newly forged creature is evident (see here). It is pale with tender pink feet and lime green highlights. Fluid is pumped into the wing veins and they expand down and out (see here & here) with the aide of Ma Gravity. The crumpled neo-wings look somewhat like bubble wrap at this stage (see here).

It takes a good 15 minutes for the wings to reach their full extension. For a moment, the past stands with the future as the crisp new adult ventures away from its old casing. It eventually moves over onto the tree bark and climbs higher up the tree to complete the drying process.

Within a few short hours, the once tender wing membranes become rigid and clear. Hardening of the exoskeleton darkens the shade to a deep mottled green and the creature is ready to enter into a Dog Day afternoon as a noisy songster.

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