This pretty, but very thin beetle is called a Slender Lizard Beetle (Acropteroxys gracilis). The adults are fond of pollen and leaves of herbaceous plants. The larvae bore into the stems of herbaceous plants and feed there. They are found east of the Rocky's and are very tiny at up to 3/8 of an inch. Look for them along roadsides and near woodland areas...or in your garden like I found this one.
They will overwinter in the stems of plants such as Joe-Pye Weed, Sneezeweed and Boneset. These beetles were originally in their own family of Languriidae....now they are included with the Pleasing Fungus Beetles in the family Erotylidae.