Black spiny-tailed iguanas (Ctenosaura similis), invasive, exotic lizards native to Mexico and Central America, were studied on Gasparilla Island, Lee and Charlotte Counties, Florida, and found, during midwinter, to make extensive use of the fruit of Brazilian pepper (Schinus terebinthifolius), an exotic, invasive plant native to northern South America. The iguanas also find shelter and excavate burrows in thickets of Brazilian pepper. Seeds of the Brazilian pepper pass through the iguana's digestive tract intact and are likely deposited with a bit of fertilizer in areas conducive to the growth of the plant. This apparent mutualistic association is most significant to the iguanas in that the fruit of Brazilian pepper is available when the iguanas are under stress due to cold weather and short days and when other foods are limited. Control of Brazilian pepper may help control iguana populations.