1. Diversity of Insects Arthropods make up about three-fourths of all named animal species. About 80 percent of arthropods are insects. Insects and Their Relatives Copyright © McGraw-Hill Education

2. External Features Insects have three body areas – the head, thorax, and abdomen. Head structures include antennae, compound eyes, simple eyes, and mouthparts. Insects have three pairs of legs, and some have wings. Insects and Their Relatives Copyright © McGraw-Hill Education

3. Insect Adaptations Legs Insect legs are adapted to a variety of functions. Legs with claws to dig in soil or crawl under bark. Sticky pads on the ends of walking legs to walk upside down. Legs adapted for collecting pollen Legs adapted to jumping Legs adapted to skimming over the surface of water Insects and Their Relatives Copyright © McGraw-Hill Education

4. Insect Adaptations Mouthparts Insect mouthparts are adapted to the food they eat. Long tubes for drinking nectar Sponging or lapping parts for taking up liquids Piercing mouthparts for feeding on plant juices or prey Insects and Their Relatives Copyright © McGraw-Hill Education

5. Insect Adaptations Wings Insect wings are outgrowths of the body wall. Wings are formed of a thin double membrane of chitin, and they have rigid veins that give the wings strength. Insects and Their Relatives Copyright © McGraw-Hill Education

6. Insect Adaptations Sense organs Insect have a variety of adaptations in their sense organs. Hairlike structures that are sensitive to touch, pressure, vibration, and odor Detect airborne sounds with their tympanic organs Chemical receptors for taste and smell are located on mouthparts, antennae, or legs. Insects and Their Relatives Copyright © McGraw-Hill Education

7. Insect Adaptations Metamorphosis Most insects undergo metamorphosis, a series of major changes from larval form to adult form. Most insects develop through the four stages of complete metamorphosis – egg, larva, pupa (nonfeeding stage), and adult. Insects and Their Relatives Copyright © McGraw-Hill Education

8. Insect Adaptations Metamorphosis Some insects undergo incomplete metamorphosis. Eggs hatch into nymphs – immature forms that look like small adults without fully developed wings. Nymphs molt several times to become adults. Insects and Their Relatives Copyright © McGraw-Hill Education

9. Insect Adaptations Insect societies Insects such as honeybees, ants, and termites organize into social groups and cooperate in activities necessary for their survival. Some insect societies have castes, groups of individuals who perform certain tasks. Insects and Their Relatives Copyright © McGraw-Hill Education

10. Insect Adaptations Insects and humans Insects pollinate most flowering plants. Produce honey and silk Serve as food for fishes, birds, and other animals Can also be harmful or parasitic to humans Insects and Their Relatives Copyright © McGraw-Hill Education

11. Centipedes and Millipedes Centipedes: Class Chilopoda Long, segmented bodies Each segment has one pair of legs First pair of appendages is modified into a poisonous claw, for killing prey Insects and Their Relatives Copyright © McGraw-Hill Education

12. Centipedes and Millipedes Millipedes: Two pairs of appendages per segment Herbivorous No poisonous claws Insects and Their Relatives Copyright © McGraw-Hill Education

13. Evolution of Arthropods Trilobites, abundant in the mid-Cambrian, were early arthropods. Tardigrades, also known as water bears, also are related to arthropods, but less so than trilobites. Insects and Their Relatives Copyright © McGraw-Hill Education