2004-08-06 / Columnists

Drawing On Science

by Stephen Yaeger


At this time of year two of our most familiar insects appear: Cicadas and Fireflies. Some people refer to Cicadas as locusts, but they are not in the locust family. It is because of their numbers that they became to be known as locusts. There are many species of Cicadas. A few weeks ago what is known as the Periodical Cicada or 17-Year Locust emerged from the ground in nearby regions. Our Cicada is sometimes known as the Annual Cicada or Dogday Harvestfly (because it appears in the hot ‘dogdays’ of summer). Actually it takes two years for this guy to emerge from its burrow, but because some of the life cycles overlap we see, that is hear, them every year. This Cicada is black with green markings. Its transparent wings are also green, and they have a span of three inches. The insect’s body has a length of a little more than one and one-half inches.

The most common thing about the Cicadas is their high, shrieking, saw-like sounds. Only the male makes the sound, which begins with a low ‘chee-chee-chee….’ This fact that the male Cicada is the sound maker was known by an ancient poet when he wrote, “Happy are the Cicadas’ lives/Because they all have voiceless wives.” The sound slowly rises and then lowers to silence. He is interested in attracting a good-looking (OK, so I might be stretching it a little) female Cicada for mating purposes. Males and females can be distinguished by taking a good look at their abdomens. A streamlined abdomen coming to a point indicates that you are looking at a female. The male’s abdomen is wider and cigar-shaped, with a more or less rounded tip. While you have the male belly-side up take a look at the two membranous plates lying flat on the belly. These are the sound makers. Each one is attached to muscles, which the insect uses to vibrate the plates. The vibrations result in the sound you hear. They only sing during the day (Imagine if they made that racket at night!). Cicadas are perhaps the loudest singers of all insects.

The life cycle of Cicadas is quite intriguing. When a female is attracted to a male, mating occurs almost immediately. Unfortunately once the male has passed on his genes, he dies! After mating, the female will cut open a soft twig with her ovipositor (OH-va-po-sitter). Once she has made a successful opening, she deposits her eggs in the twig. Then she, too, dies! In about six weeks the eggs hatch releasing Cicada nymphs. The life cycle follows what is known as incomplete metamorphosis —there is no pupa or cocoon stage. The nymph looks like an adult, but it cannot fly. The nymph will leave the twig and climb down to the tree’s base where it will proceed to burrow into the ground. Using their long, piercing and sucking mouthparts, nymphs spend the winter sucking juices from the tender roots of trees. In the summer of the second or third year, the nymph will crawl out of the ground, climb the host tree, and split its exoskeleton down the mid-back. Out comes the adult Cicada leaving its nymph exoskeleton hanging there. It slowly pumps blood into its wings and takes off to produce another generation.

Cicadas are like meat and potatoes to birds and other animals that relish them. The female Cicada Killer is a large, menacing wasp. It will hunt, sting, and paralyze a Cicada. It then takes the luckless insect in its legs and flies back to a burrow where she has prepared about six cells. Keep in mind that the Cicada weighs about three times as much as the wasp! Once back at the burrow the wasp deposits the Cicada in one of the cells. It then lays an egg on top of the paralyzed insect and flies off to seek more Cicadas until all of its cells are full. The burrow is then covered and the wasp dies. The wasp larva that emerges from its egg bores its way into the paralyzed Cicada and will then spend its time eating its way out through the winter. And you thought the movie Alien was original.

Fireflies are bioluminescent (bio-lu-men-ES-cent) insects, which are magical to observe. Bioluminescence means ‘living light.’ Fireflies, also known as lightning bugs, are actually beetles and there are a number of species of these insects. The ability to make light is due to an enzyme known as luciferase (lu-CI-fer-az), which reacts with other chemicals, luciferin and ATP (a substance that stores energy in cells).

This process of producing ‘cold’ light occurs in specialized organs. The organs are located in the yellow or greenish areas near the end of the abdomen of the insect. In most species of fireflies the light is used to attract the female. When you see the lights it is most likely the male signaling for some good-looking female to react. The female does not fly as much as the male and prefers to remain in vegetation. She signals the male by producing her own light. When the male sees her signal, he will respond. This signaling between the two will continue until they meet and mate. In some species the female continues to signal until the male comes close enough for her to have a good meal—him! After mating, the female will deposit her eggs within two days on or just below the ground. Fireflies undergo complete metamorphosis: egg to larva (does not look anything like the adult) to pupa to adult. When the larvae hatch they will begin to feed on other small insects and snails. This feeding process continues on into the fall and when winter arrives the larvae hibernate in underground burrows. In the spring the larvae awake, continue to feed and when the first signs of summer arrives the larvae make small pods of soil in which they pupate. When they become adults they mate. It is at this time that we see these magical lightning bugs. Questions? E-mail Steve: Drawingonscience@aol.com.

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