The spined micrathena is one of three species of spiny orbweavers (genus Micrathena) in Missouri. Its colors vary from whitish to yellowish, mottled with black or brown. The ten-spined, chunky abdomen sets the female spined micrathena apart from all other spiders. The carapace is amber, and the legs are glossy black.
Males of this species are seldom seen. They are much smaller and do not spin webs. Their abdomens lack spines and are instead simply elongated and dark. Most people who see them find them courting in the webs of females.
Orbweavers, including this one, spin wheel-shaped webs that are usually positioned vertically. This species tends to hang with its "back" or "top" toward the ground and the spinnerets pointing upward, with the abdomen looking like a tiny pyramid. Also like other orbweavers, Micrathena gracilis typically has one very long silk thread leading to a leaf or branch above the web. This is the spider's escape line, and it comes in handy when a bird or a hiker blunders into the web.
Similar species: Two other species of Micrathena occur in Missouri, the arrowshaped micrathena (M. sagittata) and the white micrathena (M. mitrata). The arrowhead spider (Verrucosa arenata) might also be confused with micrathena spiders. The females of these species are all easily distinguished by comparing photos.