The horseshoe crab is the only blue-blooded animal. The reason why the blood of horseshoe crabs is blue is because the blood contains heavy metal ions copper, which turns blue when it encounters oxygen. The horseshoe crab is a second-level protected animal in my country. Its blood is more expensive than gold, costing US$15,000 per liter, which is equivalent to about 100,000 RMB.

In addition to horseshoe crabs, the Ocanquichar people in Chile are also "blue-blooded people" who live year-round. In hypoxic areas above 6,500 meters, the hemoglobin in the body appears blue in this hypoxic area. However, this phenomenon is caused by a genetic mutation caused by a lack of iron in the blood and an excess of copper. It is an example of mutation in the population. .