Insects

Insects (also called cayayaan) are a class of animals belonging to the phylum Arthropoda (animals with a hard external skeleton and segmented limbs). Their key characteristics are a body divided into three sections—head, thorax, and abdomen—and six legs attached to the thorax. Most adult insects also have two pairs of wings, though many species lack wings or have only one pair.

Insects are the most diverse group of animals known on land. They are found in nearly every terrestrial habitat: forests, grasslands, freshwater, and human dwellings. They are absent only from open ocean. The number of named species is in the hundreds of thousands, while scientists estimate that many more species remain undescribed.

Body structure

The head bears compound eyes made up of many tiny lens units, two antennae that serve smell and touch, and mouthparts. The mouthparts vary with feeding mode: plant-eaters have chewing mouthparts, while those that feed on liquids have a long, tube-like proboscis. The thorax bears six legs and wings. The abdomen contains the digestive and reproductive organs.

The body surface is covered by a hard exoskeleton made of chitin. This skeleton protects the body from injury and water loss, but does not grow; therefore insects must shed their old skeleton many times as they grow (ecdysis).

Growth and reproduction

Most insects reproduce sexually. Development follows two patterns. Complete metamorphosis occurs in butterflies, flies, beetles, and ants: the egg hatches into a larva, which then pupates, and finally emerges as an adult completely different from the larva. Incomplete metamorphosis occurs in grasshoppers and lice: the hatchling resembles the adult and grows through gradual stages without a pupal phase.

Ecological role and human interaction

Insects play important ecological roles. Ants, butterflies, and some flies pollinate plants, affecting fruit and crop production. Other species break down plant and animal matter, returning nutrients to the soil. They are also food for birds, fish, and other animals.

On the other hand, many species affect human health and economy. Mosquitoes transmit diseases including malaria and dengue; lice spread gastrointestinal diseases. Grasshoppers and agricultural pests can destroy crops. Farmers and health authorities use integrated methods: insecticidal chemicals, habitat modification (such as crop rotation), and biological control using natural enemies of pest insects.