The spider genus Micrathena contains more than a hundred species, most of them Neotropical woodland orb-weavers. Only three species occur in the eastern United States: females of M. gracilis (the Spined Micrathena) have five pairs of conical tubercles / spines on the abdomen, female M. mitrata have two short posterior pairs, and female M. sagittata (the Arrow-shaped Micrathena) have three pairs. Species with extremely long spines evolved at least eight times in the Micrathena genus and likely function as anti-predator defenses.