Difference Between Insects and Arachnids

Main Difference – Insects vs Arachnids

Arthropoda is a phylum that consists of invertebrates with jointed appendages or legs. Arthropods are triploblastic, haemocoelomic animals. They consist of a segmented body with a head, thorax, and abdomen. They also consist of a chitinuous exoskeleton. Arthropods are the most successful phylum on earth. Insects and arachnids are two classes of the phylum Arthropoda. Both insects and arachnids are mainly terrestrial animals. Some of them live as parasites. The main difference between insects and arachnids is that insects have six legs and up to four wings whereas arachnids have eight legs.

Key Areas Covered

1. What are Insects
      – Definition, Characteristics, Examples
2. What are Arachnids
      – Definition, Characteristics, Examples
3. What are the Similarities Between Insects and Arachnids
      – Outline of Common Features
4. What is the Difference Between Insects and Arachnids
      – Comparison of Key Differences

Key Terms: Antennae, Arachnids, Arthropoda, Exoskeleton, Eyes, Insects, Invertebrates, Jointed Appendages, Segmented Body, Wings

What are Insects

Insects are small arthropods possessing six legs and one or two pairs of wings. Typically, insects are small invertebrate animals. Some insects are invisible, and the others can be about 7 inches long. Their body is covered with an exoskeleton made up of chitin. The body of insects is composed of three sections: head, thorax, and abdomen. Six legs are connected to the abdomen of insects. Some insects contain wings connected to the thorax. A pair of antennae can be found in the head. Insects also contain a pair of compound eyes in the head. An insect is shown in figure 1.

Difference Between Insects and Arachnids

Figure 1: A whopper

Insects undergo complete metamorphosis. Young insects that are called nymph are born from eggs. As the nymph grows, a new outer covering is formed around the body called the exoskeleton. The nymph shed the old outer covering for its further growth. This process is called molting. Termites, ants, bees, wasps, and butterflies are examples of insects.

What are Arachnids

Arachnids are wingless arthropods, consisting of a body with two segments: cephalothorax and abdomen. Archanis also have eight appendages and no antennae. Over 100, 000 species of arachnids have been identified all over the world. Arachnids have simple eyes. They hatch eggs but, do not undergo metamorphosis. The typical body structure of an arachnid is shown in figure 2.

Figure 2: Arachnid Body Structure
Four pairs of legs, (2) Cephalothorax, (3) Abdomen

Arachnids are cold-blooded animals whose blood temperature depends on the temperature of the environment. Their blood is blue in color since it contains hemocyanin. They feed on the body fluids of the prey. Therefore, arachnids are carnivorous animals. Some arachnids make nests.

Similarities Between Insects and Arachnids

Both Insects and arachnids are invertebrates that belong to the phylum Arthropoda.
Both insects and arachnids have joint legs.
The body of both insects and arachnids is segmented.
Both insects and arachnids have a chitinuous
Both insects and arachnids are mainly terrestrial.
Both insects and arachnids are triploblastic, haemocelomic animals with bilateral symmetry.
Both insects and arachnids have compound eyes and antennae.
Both insects and arachnids have a complete digestive system.
Both insects and arachnids have an open circulatory system.
Both insects and arachnids are cold-blooded.
The excretion of insects and arachnids occurs through Malpighian tubules.
The nervous system of both insects and arachnids is composed of a brain and a ventral nerve cord.
Both insects and arachnids are unisexual animals, e., both sexes are separated.

Definition

Insects: Insects are small arthropods who possess six legs and one or two pairs of wings.

Arachnids: Arachnids are wingless arthropods, having a body with cephalothorax, abdomen, eight appendages, and no antennae.

Habitat

Insects: Insects are mostly terrestrial. Some insects can be aquatic and parasitic.

Arachnids: Arachnids are mainly terrestrial, and some are parasitic.

Appendages

Insects: Insects consist of three pairs of appendages.

Arachnids: Arachnids consist of four pairs of appendages.

Wings

Insects: Many insects have wings.

Arachnids: Arachnids do not have wings.

Mouthparts

Insects: Insects possess mandibles.

Arachnids: Arachnids possess chelicerae.

Division of the Body

Insects: The body of insects is divided into head, thorax, and abdomen.

Arachnids: The body of the arachnids is divided into cephalothorax and abdomen.

Antenna

Insects: Insects have one pair of antenna.

Arachnids: Arachnids do not have an antenna.

Eye

Insects: Insects have compound eyes.

Arachnids: Arachnids have one to six pairs of simple eyes.

Respiration

Insects: Respiration of insects occurs through the trachea.

Arachnids: Respiration of arachnids occurs through trachea and book lungs.

Blood Color

Insects: Insects have colorless blood.

Arachnids: Arachnids have blue color blood.

Metamorphosis

Insects: Insects undergo complete metamorphosis.

Arachnids: Arachnids undergo a series of molts.

Examples

Insects: Butterfly, beetle, bee, ant, fly, termite, grasshopper, true bugs, and louse are examples of insects.

Arachnids: Spider, acari, amblypygid, and scorpions are examples of arachnids.

Conclusion

Insects and arachnids are two types of arthropods with jointed appendages. The main difference between insects and arachnids is the anatomical structure of each type of animals. Insects have six legs and wings. Arachnids have eight legs and no wings. There are some other differences of the body of insects and arachnids.

Reference:

1.” What are insects?” Australian Museum, Available here.
2.“Arachnids.” Education in India, Available here.

Image Courtesy:

1. “Spider-characteristics” By Kaldari – Own work by uploader. Spider image from CDC Public Health Image Library (public domain).[1], Public Domain) via Commons Wikimedia
2. “Close Whopper New Insect Insect” (Public Domain) via MaxPixel