No, Xiphosuras are usually not harmful to humans. While they have a hard exoskeleton and a long, pointed tail, their primary defense mechanism is to flip themselves over and push themselves back into the water with their legs. However, remember that treating horseshoe crabs with care and respect is critical. They may use their tail to defend themselves when provoked, potentially injuring a human or another animal. Furthermore, some people may be allergic to horseshoe crabs.