Missouri has three species of micrathena spiders, as a group called spiny orbweavers. As orbweavers, they spin intricate, circular webs. All three species have some combination of pointy, conical tubercles on their bodies. Because males are small and rarely seen, the following descriptions refer to females, which are commonly seen resting in their webs. All have glossy black legs.
M. gracilis, called the spined micrathena or spiny-bellied orb weaver, has 5 pairs of black tubercles and a white and black (or yellowish and brown-black) mottled abdomen. It is the most commonly encountered micrathena in Missouri.
M. mitrata, the white micrathena, has 2 short pairs of tubercles and a white abdomen with a few distinct black blotches on the upper side. It an odd way, it looks like it's wearing a turban, which is exactly what the species name "mitrata" refers to.
M. sagittata, the arrowshaped micrathena, has striking reddish, black, and yellow colors and has 3 pairs of tubercles. The pair of tubercles at the back end of the abdomen are rather large, forming two corners of the triangular (“arrow-shaped”) body. With a little imagination, this spider suggests a hard-rocking "Flying V" electric guitar.