The horseshoe crab's thorn is poisonous when stung. The thorns of horseshoe crabs contain a kind of venom. When the thorns come into contact with the skin of humans or other animals, the venom will enter the body and cause symptoms such as redness, swelling, itching, and pain. If exposed to a large amount, it may also cause serious symptoms such as difficulty breathing and rapid heartbeat.

Therefore, if you are stung by a horseshoe crab, it is recommended to seek medical treatment in time to avoid serious consequences.