WHY do scorpions have blue blood?

 Scorpion blood does not contain hemoglobin, which is the iron-containing protein found in the blood of vertebrates. Instead, it contains hemocyanin, which is an analog of hemoglobin found in the blood of some invertebrates. Hemocyanin, unlike hemoglobin, contains copper instead of iron.

When hemocyanin comes into contact with air, the copper in it turns blue. Hemocyanin is responsible for transporting oxygen to the tissues in scorpions and other invertebrates. When it binds with oxygen, it loses its blue color, just like how hemoglobin turns red when it binds with oxygen.

This difference in the composition of blood is one of the many adaptations that allow scorpions and other invertebrates to survive in their environments. Despite the difference in blood composition, scorpions still rely on their circulatory system to transport oxygen and nutrients throughout their bodies, just like vertebrates do with hemoglobin.