How do insects differ from crustaceans such as crabs and lobsters?

Insects and crustaceans are both members of the phylum Arthropoda, but they belong to distinct subphyla and exhibit significant biological differences.1

Key Differences

• Respiratory Systems: Most crustaceans are aquatic and utilize gills for gas exchange. In contrast, insects are primarily terrestrial and possess a tracheal system, a network of tiny tubes that delivers oxygen directly to their tissues, eliminating the need for respiratory pigments in their blood.23
• Circulatory Pigments: The blood of many large crustaceans contains hemocyanin, a blue, copper-based oxygen-carrying pigment. Insects generally lack respiratory pigments because their tracheal system handles oxygen transport directly.3
• Appendages: Crustaceans are characterized by having two pairs of appendages—antennules and antennae—in front of the mouth, as well as paired appendages near the mouth that function as jaws.4
• Endocrine Systems: While both groups use hormones to regulate functions like molting, their mechanisms differ. For example, crustaceans possess an androgenic gland that controls male sexual differentiation, a structure not found in insects.5

While both groups have evolved to occupy diverse habitats, crustaceans remain primarily aquatic, whereas insects have successfully colonized nearly all terrestrial environments.16