June's Bugs

Natural History, June, 1999

The warm summer days are filled with buzzing insects. After a long winter, many have only a few weeks, days, or hours to mate, and the longer, warmer days put them in the mood.

DRAGONFLIES

In the early days of June, near marshes and ponds throughout North America, dragonfly and damselfly nymphs begin to crawl out of their aquatic homes, envelop themselves in cocoons, and eventually emerge as flying insects. Look for their empty brown cocoon husks on shoreline vegetation and pier posts. The migratory one- to five-inch green darner (Anax junius) is found all over North America. Its large compound eyes and rotary head allow virtually a 360 [degrees] field of view.

These agile flyers have been clocked at thirty-six miles an hour, and their efficient design has captured the interest of aeronautical engineers and bioengineers alike. Darners are mostly iridescent green, with a faint gold shimmer on their wings; the males' abdomens are metallic blue, and the females' violet. Since these creatures mate in fight, it is common to see a tandem couple buzzing around, the male holding on to the female with a special set of claspers and not letting go--sometimes for days--in order to keep other males from mating with her. The female is often seen skimming the surface of the water, touching it from time to time as she scatters her eggs. Dragonflies actually catch their prey--mainly mosquitoes--with their legs and then transfer the food to their mouths.

Check out the Texas Agricultural Experimental Station's Digital Dragonflies Web site at www.dragonflies. org to view scanned images of different types of dragonflies and damselflies.

July 8-11: Dragonfly Society of the Americas Annual Meeting

Paul Smiths College, NY, or www.afn.org/~iori/dsaintro. html. For other dragonfly and damselfly information, go to the Odonata Information Network (www. afn.org/~iori).

PESTS

Summers would seem too easy without the bothersome bumps brought on by biting and stinging bugs. Although some species of mosquito act as a conduit for spreading diseases, in developed nations they are mostly just an annoyance--mainly to mammals. However, these insects play an important role in the health of the ecosystems they inhabit: As wriggly aquatic larvae, they are an important source of food for fish. As adults, mosquitoes are vital food for dragonflies and damselflies and are a favorite meal for birds as well. Mosquito wings beat six hundred times a second, generating that familiar high-pitched whine. At night, only the female goes in search of a blood meal, which she needs to produce her eggs. First she looks for large dark objects that move. Should she notice that the object is giving off heat and carbon dioxide, as all mammals do, she'll stay.

The American and black horseflies are abuzz in the summer months. Together, these large biting flies inhabit every possible ecological niche in North America, from open grassland to saltwater marsh, sparing only parts of southern California. The females inflict a painful bite as they quickly slice the skin of their victims with bladelike mouthparts and then feed on the blood. Because their saliva contains an anticoagulant, the wound can bleed for several minutes. Don't worry about looking for these biting bugs: they'll be sure to come looking for you.

Zoos will be hosting bug fests throughout the summer, often including cockroach races. These hardy household scavengers, it has been said, would survive a nuclear war. Recent research has shown they actually are much more resistant to harmful radiation than are other living things.

CICADAS

Cicadas come out in full force during the hot days of June in the South and during July and August in other regions. The high-pitched chittering of the male cicada is made by an organ called a timbal, located on its abdomen; this muscle-controlled, drumhead-like structure vibrates up to 390 times per second. Female cicadas do not have timbals, although they sometimes use their wings to make clicking and snapping sounds. Each species of cicada has its own song and prefers a particular time of day in which to sing it.

Dog-day and grand western cicadas sing on their own, but periodical cicadas, with life cycles of thirteen or seventeen years, use teamwork, and the males form a huge, deafening, female-attracting chorus. Usually, over a period of about two weeks, the chorus will have drawn a significant number of synchronized male calls and will sound like a single shrill voice. Mating occurs during this time. Periodical cicadas are also one of the few insects that have no morphological or behavioral defense against predation, but scientists suppose that hatching en masse works as a kind of species survival strategy: predators quickly eat their fill from the millions of emerging cicadas and leave the remaining individuals alone, a passive tactic referred to as predator satiation.

To find out more about cicadas, contact the University of Michigan Museum of Zoology, Insect Division, 1109 Geddes Ave., Ann Arbor, MI 48109, or go to insects.ummz.lsa.umich.edu.