These striking spiders look like they ought to be related to the spiny orb-weaver (Gasteracantha sp). They are in the same family (Araneidae) but a different genus (Micrathena). They have fewer spines than Gasteracantha (and, again, probably a bunch of smaller details, like the number of hairs on the thorax or which way some microscopic structure points).
Arrow-shaped micrathena spiders live all over the eastern US, as far north as Maine and as far west as eastern Kansas. They are one of only three Micrathena species found in North America. They are a small (1 cm), sexually dimorphic spider (females larger and more visually conspicuous, with larger spikes), generally patterned red and black with distinctive spines on the abdomen which give the spider its characteristic, arrow-like shape.
They are diurnal, taking down and eating their web at night and building a new one each day, and eat pretty much anything they can catch. It is thought that the bright yellow (“Pikachu-like”) abdomen of the females may help attract prey, and the spikes may make the spider difficult for birds and other predators to swallow.
Like most spiders, this species looks scary, but is totally harmless to humans.