🐛 Insects: Earth's Most Diverse Animals
Building on our introduction — let's dive deep into the anatomy, life cycles, diversity, and ecological importance of Class Insecta.
🔄 Recall from Last Lesson
In our previous lesson, we briefly introduced insects as part of the arthropod phylum. You learned that they have jointed legs, an exoskeleton, and segmented bodies. Now, let's explore insects in much greater detail!
1. What Exactly Is an Insect?
Insects (from Latin insectum, meaning "cut into sections") are hexapod invertebrates belonging to the class Insecta. They are the largest group within the phylum Arthropoda (Arthropods).
Every insect shares these defining features:
- Chitinous exoskeleton — a hard outer covering made of chitin (a tough polysaccharide)
- A three-part body: head, thorax, and abdomen
- Three pairs of jointed legs (6 legs total)
- Compound (faceted) eyes made of many tiny lenses
- One pair of antennae
🔢 By the Numbers: Over 1 million insect species have been described — that's more than half of all known animal species! Scientists estimate the true total could be around 6 million species.
🕷️ Insect or NOT an Insect?
| Organism | Legs | Body Parts | Insect? |
|---|---|---|---|
| 🐝 Bee | 6 | 3 | ✅ Yes |
| 🦋 Butterfly | 6 | 3 | ✅ Yes |
| 🕷️ Spider | 8 | 2 | ❌ No |
| 🦂 Scorpion | 8 | 2 | ❌ No |
| 🐜 Ant | 6 | 3 | ✅ Yes |
| Centipede | 30–354 | Many | ❌ No |
| 🦗 Cricket | 6 | 3 | ✅ Yes |
Spiders, ticks, scorpions, and centipedes are arthropods but not insects. Centipedes have far more than six legs!