There are two species of prickly pear growing on Ascension, Opuntia monacantha and Opuntia stricta var. dillenii. Prickly pears are cacti which are dispersed across the island. Whilst the prickly pear was originally introduced in order to enrich soil and inhibit moisture evaporation, it started to spread very quickly. A moth Cactoblastis cactorum was subsequently introduced in 1974 as a way of controlling the expansion of the plant and is believed to be having success in halting its spread.