Abstract
Morphological changes of flowers and insect visitors were observed to investigate pollinator of Caesalpinia decapetala. The flowers of C. decapetala are protandrous. Functionally, the flower is changed from male to female. As a male, pollen grain is released after anther dehisced while style is immature. After completed pollen grain release, the style starts to lengthen. It helps the stigma to easily touch the carpenter bee's thorax covered with pollen grain. At this time, flower functions as a female. The majority of taxa and individuals observed were Hymenoptera. The most frequent visitor was the Xylocopa appendiculata circumvolans, carpenter bee. Carpenter bees exhibited only typical pollinator behavior among flower visitors, with touching reproductive organs and seeking nectar at the same time. The pollination behavior is as follows. Soon after carpenter bees perceived guide mark, they foraged rightward and grasped style and stamens with legs and they inserted proboscis into standard petal to seek nectar. With this behavior, the pollen grains of the male flower transfer to the ventral thorax of the carpenter bee. As the carpenter bee moves to another female flower, the deposited pollen grains are delivered to the stigma.