Michael Deniger, age 12, of Coventry, Rhode Island, for his question:

How long  have insects been roaming around?

The most dependable evidence comes from fossils. But insects do not make good fossils, because, as a rule, their small fragile bodies soon decay and break down to enrich the soil.. Scientists suspect that perhaps a million modern species exist, though only about 800,000 have been identified. The fossil record goes back more than 250 million years, though fossils of fewer than 20,000 of the ancient species have been found.

Scientists classify the modern insect world in 25 or 30 orders. They have fossil evidence to prove that ancestors of all these orders were roaming around during the Tertiary Period. This was about 60 million years ago, when the dinosaurs were departing. Some of this evidence is preserved in glassy amber. These gobs of resin oozed from trees that grew around the Baltic Sea. Ants and other insects were trapped in the goo and perfectly preserved as the amber hardened. Several were exactly like modern ant species, others are extinct.

Ants, bees and wasps are classified in the order Hymenoptera, the membrane winged insects. The fossil record proves that ancestors of this order roamed around during the Jurassic Period, about 180 million years ago. They shared their world with the first flowering plants and ancestral moths and butterflies.

Ancestral sawflies and members of the true bug order were around during the Triassic Period, about 230 million years ago. They shared their world with numerous species that arrived about 280 million years ago, during the cool, dry Permian Period. Fossils from this period include ancestral stoneflies and mayflies, beetles and weevils, locusts and grasshoppers.

We know that a few species arrived even earlier, during the Carboniferous Period, named for the scrawny forests that thrived in vast areas of soggy swampland. Later this vegetation was carbonized to for:o coal. Most insects of those ancient times perished and soon decayed in the mild, moist environment. But some specimens fell into stagnant waters, where there was too little oxygen to support decay bacteria. These were pressurized and fossilized between layers of coal.

The most famous Carboniferous insect was a dragonfly type. He zoomed through the ferny forests on gauzy wings 30 inches wide. He shared his early world with a smaller long legged insect who had four gauzy flying wings, plus a pair of undeveloped wings. This species became extinct. At least one other Carboniferous insect did not. He was a roach, a sturdy ancestor of the cockroach order.

The roaches and dragonflies of 300 million years ago were already well developed. Obviously they came from ancestors similar to themselves, but so far none of their fossils have been found. Scientists suspect that there may have been primitive insects around as long as 400 million years. Their remote ancestors may have been closely related to crustaceans or wormy creatures of the sea.