They are here to stay

Jan 22, 2008 21:56 GMT  ·  By

1.There are about 900,000 described species of insects, forming 80% of the described animal species, and scientists evaluate their actual number to be somewhere between 2 to 10 million species, including unknown species. Calculating the total number of insects on the globe, researchers found it overpassed by 200 billion times the number of humans. Insects live in various environments, from hot volcanic spring and hot deserts to frozen tundra, rain forests, the top of the mountains and caves.

2.The insect exoskeleton is made of kitin, a horny brown material, flexible and permeable, stiffened by a protein called sclerotin. Its resistance to water is given by wax layers. But for growing, the insect must expel the old cuticle and replace it with a bigger one. The old cuticle turns thinner as its kitin is dissolved and absorbed by the insect's body. The old cuticle cracks, usually on the dorsal side, and the insect gets out with the new shiny and soft one. The insect absorbs water or air to swell and stretch the new cuticle. In several hours, the new exoskeleton hardens. During the period of soft cuticle, insects are vulnerable to predators. A too large insect would collapse under its own weight in this period. That's why the heaviest insect is Hercules' beetle, which weighs 100g (0.2 pounds), as much as a mouse. A dragonfly 290 million years old had a wingspan of 68cm (2.3 ft).

The size of the insects is also limited by the tracheal tubes: they work well for small bodies, but with the increasing body, the air tends to stagnate.

3.Few insects live for several years, and most have a lifespan comprised in months, weeks or days. Rapid generations in the case of mosquitoes allow them to take advantage on temporary pools. Because insects have such rapid alternations of generations, they also evolve very quickly.

4.How old are the insects? Snow fleas appeared 380 million years ago. Cockroaches are 360 million years old, dragonflies 340 MY old, grasshoppers 300 MY, caddisflies, stoneflies and mayflies 280 MY, bugs and antlions 260 MY, scorpion flies, bristletails and thrips 250 MY, beetles and stick insects 240 MY, wasps 230 MY, earwigs and flies 200 MY, butterflies 120 MY, termites and fleas 70 MY.

5.Insects are masters of the flight. They had flown 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. In butterflies, the wings are covered by colored scales. The most primitive insects do not have wings at all, they form the group called Apterygota. In the winged insects (Pterygota), wings can be found sometimes only in one sex (male fireflies are winged, females not), or some castes (in termite and ants, only sexually active males and females have wings; workers do not).

Mosquitoes can fly with the abdomen upward. Some can fly in the rain without getting soaked, by slipping between the rain droplets. Some tropical wasps and bees can fly with 72 km (45 mi) per hour, while locusts and dragonflies can fly with 45-60 km (29-37 mi) per hour. The monarch butterfly of North America makes migrations 3,200 km (2,000 mi) long. Some flies can beat their wings more than one thousand times per second, faster than a hummingbird. And even the bee has a wing beat of 230 per second. Dragonflies can fly backwards (amongst vertebrates, only hummingbirds can do this).

6.The insects' reproductive power is amazing: in warm conditions, in less than one month, a locust becomes adult and each female deposes hundreds of eggs during a season.

In a little cloud of locusts, covering 100 square km (40 square miles), there are about 70,000 tons of insects, thus several tens of billions of locusts, each weighing 2 grams. A swarm of one billion locusts can consume 3,000 tonnes of vegetation daily.

In fact, in some environments, in just one square kilometer, there live more insects than humans on the whole planet. In ecosystems, ants make 15-25% of the total animal biomass.

Just one ant colony cleanses of other insects a surface of 2-3 forest hectares. The army ants (Eciton), found in tropical America, have colonies of 100,000 to 2,000,000 individuals, that will kill and eat everything in their path, and in other species, the colonies can have 20 million individuals. Even in a bee hive, there are 80,000-100,000 individuals.

7.To store one honey kilogram (2.5 pounds), the bees of a hive must visit roughly 7 million flowers and make 240,000 km (150,000 miles), which means 10,000 flight hours.

8.Locusts and grasshoppers can jump over 10 times their length, and fleas 200 times their body length (it's like humans jumping 360 m (1,200 ft)!).

9.The feet of the insects have adhesive pads, covered with special hairs that enable them to walk on ceilings, vertical walls and even on viscous surfaces. Scientists are trying to achieve an imitation of this process.

10.The termite colonies, made of millions of individuals, build mounds that can be 7.5 m (25 feet) tall over the soil, but underground, they can be 75 m (225 feet) deep and extend hundreds of meters away. It's like people building an edifice as big as the Himalayan Mountains. These constructions have sophisticated installations of conditioned air and underground fungi gardens. And all these builders are blind!

Not only termites, but ants cultivate fungi as well. The leaf cutting ants (Atta) chop the leaves of trees and gather the leaf remains from the forest floor, carrying all into their underground nests. All is grounded into a soft mix with which they feed their underground fungi gardens. The ants maintain the gardens at the optimum values for temperature and humidity in order to get the best results. The new leaf layers are "seeded" with older material and, to increase crop production, the ants even "weed out" the layers. The production is adapted to the colony's food necessity, saving time and energy this way. The gardening implies sustained work.

11.The insect metamorphosis is an amazing phenomenon per se. Most insects experience metamorphosis: from a worm-like larva results a very different adult. The adult may not even eat at all and live just a few days.

A maggot will turn into a fly, a caterpillar - into a butterfly; it's like turning a train into a plane. The dragonfly larva lives in the water feeding on little fish and tadpoles; the adult fly will freely hunt insects. Can you imagine a human living the first 20 years swimming in the sea, and after that flying like a bird?

12.Insects have 5 eyes: three small ocelli and two big compound eyes, made of 30,000 ommatidia, photosensitive units. Flies have a sharp vision sense and reflexes ten times more rapid than ours. Many insects, like butterflies and bees, see in ultraviolet light. The eye of many insects works like a compass: bees and wasps can detect polarized light, allowing them to establish the position of the sun on the sky even when hidden by clouds. This way, they will always know how to turn back home.

13.Insects rely heavily on pheromones for communication. A male butterfly's or moth's sophisticated antennae will pick up just one molecule of pheromone, tracking a female found 11 km (7 mi) away.

Crickets, grasshopers and cicadas prefer "serenades" for attracting a mate, their ears being placed on the thorax. The sound made by male cicadas is stronger than the noise emitted by a pneumatic drill.

14.Insects are cold-blooded and, just like snakes and lizards, they take sunbaths in the morning. Some beetles are attracted by the water lilies flowers, which have a temperature 20 degrees C higher than that of the environment. Butterflies have an incorporated heating system: when requiring heat, they open their wings which act like solar panels and tilt them in the direction of the sun.

15.Some insects have special characteristics. There are butterflies that extract salt and humidity from cattle's tears and dung. Other insects possess a powerful antifreeze, enabling them to inhabit snowy peaks, eating on beetles that died of cold.

16.Although many people consider insects as being annoying, we need them. About 30% of our food depends on the pollination made by wild bees. Insects maintain the soil clean by recycling dead plants and animal matter. The soil gets fertilized and nutrients help plants grow. In Australia, Europeans brought the cattle, but the local insects did not process cattle dung, and the dung boosted the populations of bush flies, an annoyance for both people and cattle. The problem was solved by bringing dung beetles from Europe and Africa.

Some insects attack crops and carry diseases, but only 1% of the insect species are considered pests, and many produce increased damages due to the way people manage the environment. Malaria mosquitoes rarely bother the inhabitants of the rain forests, but they cause mayhem in the cities filled of pools at the edge of the forests. Crop alternation and preserving the insects' predators may control their numbers. For example, ladybirds destroy aphids, while the dragonfly larvae eat the mosquito larvae.

17.The relationship insect-plant can be really weird. Orchid mantis (Hymenopus coronatus) from southeastern Asia mimics so well a pink flower, that pollinating insects go straight into the killing arms of this predator.

The caterpillar of Cucullia artemisae mimics so well a withered flower that predator insects ignores it. The butterfly Heliconius lays its eggs on the leaves of the passion flower (Passiflora). The hatching caterpillars consume plants' leaves. As a reaction, the plant turned some of its nectar glands in small yellow structures resembling the butterfly eggs. Flying butterfly females looking for a place to lay their eggs think the place has been occupied by another female and seek for other plant. On the leaf ribs formed rigid hair that limit the caterpillar's movements. Moreover, some nectar glands attract ants and wasps that attack the caterpillars.