How do female American horseshoe crabs compare in size with males?

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Horseshoe crab (Limulus polyphemus) with a hard, rounded shell and long pointed tail lying on sandy ground. — horseshoe crab Horseshoe crab (*Limulus polyphemus*).

Female American horseshoe crabs are larger than their male counterparts. While specimens of the species Limulus polyphemus can exceed 60 cm (2 feet) in length, males typically average between 36.6 and 38.1 cm (14–15 inches), whereas females typically average between 45.7 and 48.3 cm (18–19 inches).1