Opuntia in shallow, loose soils, such as on mountain slopes. "Opuntia" spreads into large clonal colonies, which contribute to its being considered a noxious weed in some places. Animals that eat "Opuntia" include the prickly pear island snail and "Cyclura" rock iguanas. The fruit are relished by many arid land animals, chiefly birds, which thus help distribute the seeds. "Opuntia" pathogens include the sac fungus "Colletotrichum coccodes" and Sammons' Opuntia virus. The ant "Crematogaster opuntiae" and the spider "Theridion opuntia" are named because of their association with prickly pear cacti. Like most true cactus species, prickly pears are native only to
Opuntia ovaries per carpel. Placentation is parietal, and the fruit is a berry with arillate seeds. Prickly pear species can vary greatly in habit; most are shrubs, but some, such as "Opuntia echios" of the Galápagos, are trees. "O. ficus-indica" thrives in regions with mild winters having a prolonged dry spell followed by hot summers with occasional rain and relatively low humidity. A mean annual rainfall of provides good growth rates. "O. ficus-indica" proliferates in various soils ranging from sub-acid to sub-alkaline, with clay content not exceeding 15-20% and the soil well-drained. The shallow root system enables the plant to grow