More sophisticated than previously thought

Feb 27, 2008 14:37 GMT  ·  By

Only three groups of animals really fly today: insects, birds and bats. Flight requires the use of organs called wings, but their structure and functioning differ enormously from one group to another. Anyhow, all flying animals are heavier than the air and only the wings movement and the use of air currents keep them flying.

Still, flying animals have relatively lighter bodies. The insect body is crossed by a network of thin respiratory canals called tracheae, which lighten their bodies (like the air sacs and pneumatic bones of the birds).

Insects had been flying 150 million years before the first birds did, and they are the only winged invertebrates. The first flying insects could not bend their wings over their abdomen, as present-days dragonflies do.

In butterflies, the wings are covered by colored scales. The most primitive insects do not have wings at all (the group named Apterygota). In the case of the winged insects (Pterygota), wings can be detained only by one sex (male fireflies are winged, females not), or some castes (in termite and ants, only sexually active males and females have wings, while workers are wingless).

In cool weather, insects must raise their body temperature for taking off, in most cases using sun heat. Scorpionflies (Panorpa) raise their body temperature to 25o C before flying. The moth called Celerio euphorbiae can raise its body temperature by means of muscular contractions, to 30-40o C before taking off. This creature is also one of the rapidest flying insects. The emperor moth (Saturnia pavonia) raises its body temperature to 20o C before flying.

Mosquitoes can fly with the abdomen upwards even in the rain, without getting soaked, by slipping between the rain drops. Dragonflies can fly backwards (the hummingbirds are the only species that can do this, too).

Some tropical wasps and bees can reach 72 km (45 mi) per hour in flight, while locusts and dragonflies, 45-60 km (29-37 mi) per hour. The monarch butterfly of North America makes migrations 3,200 km (2,000 mi) long.

Insects have two pairs of wings, but, in many cases, just one serves for flight. The insect wing is made of a membrane swept by numerous thickened ribs. Because of the ribs, the wing does not fold during the flight. In beetles and bugs, the anterior wings, resembling a crust, are called elytra and they do not beat the air, being just protective. Mosquitoes and flies have just one pair of wings (not two), the second being turned into two organs that detect altitude and acceleration, allowing the insect to adapt permanently to the flight's parameters.

The cabbage white butterfly (Pieris) has a wing rhythm of 5-10 beats per second, the hawker dragonflies have a rhythm of 20-30 beats per second, the bumblebee (Bombus) of 123-233, the house fly (Musca), 147-220, and the honey bee (Apis) of 240-260. Midges (Chironomus) have a rhythm of 196-494. Some flies can beat their wings over 1,000 times per second, more rapidly than a hummingbird.

Mosquitoes can fly 1.5-2.5 km (0.9-1.6 mi)/h at most 5 minutes at once, with a wing rhythm of 250 beats/second. This rhythm determines their buzz and they would like not to generate it; otherwise their presence would be undetectable until they bite. Mosquitoes can execute various aerial stunts, like turns, loopings, forced landings, dives.

The rapid movement of the wings in insects was found to be based on a very rapid break down of the glycogen ("animal starch") from the muscles into the glucose which delivers the required energy through its burning.

A bee collecting nectar at a distance of 3 km (1.8 mi) off the hive spends 0.00035 g of glucose with its flight. Instead, it collects 0.004 g of glucose with the nectar (about 0.02 g).