Information on the Animal Classes Insects and Arachnids
What Are Insects?
Characteristics and Special Features of Insects:
- Invertebrates: Insects lack an internal skeleton and a backbone.
- Exoskeleton: A hard shell made of chitin protects the body from the outside.
- Three-part body: The body is divided into the head, thorax, and abdomen.
- Six legs: All adult insects have exactly six legs.
- Metamorphosis: They develop through larval stages into the adult form.
- Antennae: Insects use their antennae as touch and smell organs.
The Evolution of Insects
Insects (and spiders) are part of the arthropods. They originated around 400 million years ago and mostly live as solitary creatures, although there are also so-called “social” insects like ants and termites. They live in large numbers together in one area. There are over a million species of insects on Earth, making up about 2/3 of ALL living beings on the planet (including plants). They are perfectly adapted to their habitats, and some could even survive a nuclear war – without even “batting an antenna.”
Habitat
Where Can Insects Be Found?
Insects are highly adaptable and have conquered a wide variety of habitats. They live on or in the ground and in water.
- Above ground (bees)
- Below ground (ants)
- In qater (dragonfly larvae)
Movement
How Do Insects Move?
Insects are perfectly adapted to their environment through their unique modes of movement. They can:
- climb (ants)
- jump (fleas)
- run (bees and wasps)
- fly (fireflies)
- swim (larvae)
Diet
What do insects eat?
Insects can be either herbivores or carnivores. Some even consume their own kind (e.g., dragonflies).
- Herbivores (wood bees)
- Carnivores (hornets)
- Omnivores (earwigs)
Reproduction
How Do Insects Reproduce?
Most insects are born as caterpillars or larvae and later transform into their adult form. They undergo a pupation process and emerge as fully developed creatures from their cocoons. This process is known as metamorphosis (Greek for "transformation").
What Sets Insects Apart From Other Animal Species?
While other animal species have a skeleton made of vertebrae and a backbone, insects possess what is called an exoskeleton. This acts like a shell that holds everything together from the outside and provides support. In insects, it is also referred to as a chitin armor and can be either soft or hard. Most insects have wings.
Fun Facts
Insects in Medicine
For many of us, eating insects is a test of courage. For the Chinese, it’s just "old news." They used to nibble on dried cockroaches for stomach aches and fevers, or ladybugs for toothaches. Nowadays, there is active research on insects and spiders. Some might even lead to breakthroughs against cancer tumors or heart failure.
Species
There are about one million species of insects:
| Beetles: | 400,000 |
| Hymenoptera: | 200,000 |
| Butterflies: | 150,000 |
| Diptera: | 85,000 |
| Bugs: | 40,000 |
| Lice: | 15,000 |
| Dragonflies: | 4,900 |
| Fleas: | 2,000 |
What Are Arachnids?
Characteristics and Special Features of Arachnids:
- Invertebrates: Arachnids are part of the invertebrate group.
- Eight legs: The most notable feature is their eight legs (four pairs).
- Two-part body: Their body is typically divided into a cephalothorax and an abdomen.
- No antennae: Unlike insects, spiders do not have antennae.
- Simple eyes: Most species possess several simple eyes instead of compound eyes.
- Not insects: Biologically, they constitute a completely separate class.
The Evolution of Arachnids
Spiders, like insects, belong to the arthropods. The first arachnids existed 500 million years ago. Often, insects and spiders are grouped together, but biologically, they are distinct. Interestingly, scorpions and ticks are also classified as arachnids.
Habitat
Where Can Arachnids Be Found?
Aside from oceans and Antarctica, arachnids can thrive in nearly every environment.
- Above the ground (ticks)
- Below the ground (purseweb spiders)
- In the water (diving bell spiders)
- In caves (orbweaving cave spiders)
Movement
How Do Arachnids Move?
Arachnids can – depending on the species – walk, climb, and jump.
- climb (nursery web spiders)
- jump (jumping spiders)
- dive (diving bell spiders)
Diet
What Do Arachnids Eat?
Arachnids primarily have insects on their menu, except for the “vegetarian spider.”
- Carnivores (meat eaters)
- Herbivores (plant eaters)
Reproduction
How Do Arachnids Reproduce?
Spiders lay eggs, while scorpions give birth to their young alive.
What Distinguishes Arachnids From Other Animals?
Arachnids can be easily identified by their number of legs: They have four pairs of legs, totaling eight in all. So, if you're wondering whether you're looking at a tick or a beetle, it's best to quickly count the legs. Their bodies are typically divided into two sections: the cephalothorax and the abdomen. The mouthparts of arachnids usually include chelicerae. A notable feature of scorpions is their long tail with a stinger.
Species
There are over 110,000 species of arachnids:
| Cobweb spiders: | 51,000 |
| Mites: | 50,000 |
| Harvestmen: | 6,600 |
| Scorpions: | 2,500 |
| Camel spiders: | 1,000 |
Biodiversity
There are over 100,000 species of arachnids, each unique in its own way. They come in various sizes, some are venomous, colorful, etc. Some dig traps, others are herbivorous or live underwater. But why are there so many different types? Learn more about biodiversity.
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