Disclosed is a solid form of 4-[5-[3-chloro-5-(trifluoromethyl)phenyl]-4,5-dihydro-5- (trifluoromethyl)-3-isoxazolyl]-N-[2-oxo-2-[(2,2,2-trifluoroethyl)amino]ethyl]-1- naphthalenecarboxamide (Compound 1). Also disclosed are compositions containing a solid form of Compound 1 and methods for controlling an invertebrate pest comprising contacting the invertebrate pest or its environment with a biologically effective amount of a solid form of Compound 1 or a composition containing a solid form of Compound 1.