英文： What people like to talk about most is the love story of horseshoe crabs. Horseshoe crabs live on the sea floor and only climb to the shore when laying eggs. Summer is the breeding season of horseshoe crabs. At this time, we can often see the horseshoe crabs congregating in groups on the beach. The female horseshoe crabs carry the smaller male horseshoe crabs on their backs, inseparable like the mandarin ducks. So they have got a good name "submarine mandarin ducks".
What's more surprising is that horseshoe crabs have blue blood! The blood of most animals is red because it contains iron ions, which when combined with oxygen forms hemoglobin that makes the blood red. However, the blood of horseshoe crab contains copper ions. When copper ions combine with oxygen, hemocyanin is formed, which makes the blood blue. What's more, this blue blood solidifies when it comes into contact with bacteria. Taking advantage of the feature, people have already applied the blue blood in medicine to quickly detect bacterial infections in human tissues.