The social forms of the red imported fire ant, initially discovered in Taoyuan County in 2003, were determined based on Gp-9 allele identification. Both polygynous and monogynous colonies were found. It was also found that, in almost all of townships surveyed, there was tendency to have more polygynous nests than monogynous nests. The monogynous nests were indeed authentic monogynous nests without contamination of the cryptic b-prime allele from South America. Sequence comparison revealed that polygynous colonies in Taiwan contained either the Gp-9^B1 or Gp-9 ^B3 variant (Sinv.B1 and Sinv.B3 in GenBank) of the B allele, whereas some of the monogynous colonies contained a Gp-9^B2–like variant of the B allele (Sinv.B2 in GenBank). Gp-9 ^B1 also was found in some monogynous colonies. The scenario of a single introduction by a founding polygynous colony with all of the monogynous nests being descendents of this polygynous nest was also ruled unlikely because of the presence of the monogyne-specific B2 allele. These findings favor multiple origins of the red imported fire ant in Taiwan.