Saturday, April 11, 2009

The noise of Cicada

The cicada is a large-bodied, dark-colored, flying insect with four long, transparent wings and large eyes. When at rest, the cicada holds the wings peaked over the body like a tent. Cicadas are not locusts (locusts are a type of grasshopper). Cicadas can damage twigs when eggs are laid in the twig (unlike locusts and grasshoppers who damage plants by defoliation - leaf eating).

Like all insects, the cicada has three body parts (the head, thorax and abdomen), two large, compound eyes, clear wings, and six jointed legs. They breathe through spiracles - small holes in the abdomen. The antennae are short and bristly. Adult cicadas range in size from 1 to 2 inches (2.5 - 5 cm) long.

Kingdom Animalia (animals), Class Insecta (insects), Order Homoptera (aphids, cicadas), Family Cicadidae (all cicadas), many Genera, including Genus Magicicada (long period, red-eyed cicadas - with a 13 or 17 year life cycle) and Genus Tibicen (dog-day cicada -- with a 2 to 5 year year life cycle). Some cicadas produce sounds louder than 100 dB! They modulate their noise by wiggling their abdomens toward and away from the tree that they are on.

Cicadas eat plant sap while in their long juvenile (nymph) stage.

Males make a shrill, buzzing call by vibrating two drum-like membranes (called tymbals) covering hollow chambers on the abdomen using muscles (females do not make this noise) - they usually do this while perching high up in trees. (This is unlike grasshoppers, who make noise by rubbing their back legs together.) Male cicadas call to attract females. The loudest insect in the world is the African cicada (Brevisana brevis); it regularly produces sounds at 106.7 dB at a distance of 50 cm (this is about as loud as a power saw).

Life cycle
The cicada has the longest life cycle of any insect, ranging from 2 to 17 years. A rice-shaped egg is laid in tender twigs and plant stems. The egg hatches into a nymph (the larval stage) and drops to the ground. The nymph burrows into the soil and crawls to a tree root (using its claw-like front legs). The nymph will eat the tree's sap. The nymph stage lasts up to 17 years in periodical cicadas; dog day cicadas have a shorter life cycle. There is no pupal stage. When the nymph is fully grown and the temperature is optimal, the nymph tunnels to the surface and goes through its final molt (shedding its hard outer skin) and emerges as a winged adult. When the wings dry and harden, the cicada flies in search of a mate. Unlike many other insects, all of the periodical cicadas in an area emerge at once.

Cicada Nymph
Almost all of life time Cicadas spend underground as nymphs. They borrow into the ground at depths of about 1 feet and up to 9 feet. The young Cicadas feed on roots of trees and grass. They usually suck juices and eat younger roots. Because they live underground and need to dig through it they developed strong front legs. When Cicadas are developed you can still see that front-legs are over developed in comparison with other legs. See picture on the top. When time comes for Cicadas to go from their underground tunnels to the surface they construct an exit tunnel and emerge for their skin shedding. Before Cicada become an adult and sheds its skin, it tries to find a plant where it attaches itself with its claws. Many times their shell will remain attached to a plant long after Cicadas hatched.

Cicada Skin
Cicada Nymph has skin has yellowish color and is very tough on the surface. This skin toughness is necessary for Cicada while its being developed underground. Since it has to borrow tunnels, it’s natural to have panzer like skin. Yellowish color may be attributed to dark conditions under the ground and as a result there is no need for skin mutation that matches surroundings like we’ll find it later when Cicada hatch and becomes an adult. When Cicada hatch, its Nymph skin splits in the middle allowing adult Cicada freely mutate into flying insect. Because of its toughness Cicada skin may be seen, long after its occupant left, attached to a tree branch of a grass.