Arethaea phalangium is a species in the family Tettigoniidae ("katydids"), in the order Orthoptera ("grasshoppers, crickets, katydids"). The species is known generally as the "eastern thread-leg katydid". It is found in North America.
References
Further reading Capinera J.L, Scott R.D., Walker T.J. (2004). Field Guide to Grasshoppers, Katydids, and Crickets of the United States. Cornell University Press. Otte, Daniel (1997). "Tettigonioidea". Orthoptera Species File 7, 373.