A method for preparing a criterion for identifying the habitat of insects of the same kind, comprising the steps of: (a) determining the nucleotide sequences of DNA of one or more insects from two or more habitats; (b) aligning the nucleotide sequences determined in said step (a); (c) eliminating sites consisting of one or more nucleotides conserved in all of the nucleotide sequences aligned in said step (b) from the nucleotide sequences; (d) defining all or a part of the sites remaining upon elimination in said step (c) as type-discriminating sites; (e) comparing nucleotides corresponding to each other in the type-discriminating sites obtained in said step (d) to classify completely identical type-discriminating sites as the same type and incompletely identical type-discriminating sites as one or more different types; and (f) determining the habitat of each type classified in said step (e) on the basis of the habitats of insects belonging to each type, thereby defining the type-discriminating site of each type as a criterion.