Although it has a reputation for being a spiky and very well defended plant, the humble cactus is the food of choice for several birds, insects and other animals, as well as being the food of last resort for several more. Many cacti are highly fleshy plants with a large water storage capacity, making them an excellent choice for any creature, including humans, that is low on water and other nutrients while out in the desert.
Several species of animal will eat cactus, although in the majority of cases it is a plant of last resort thanks to its prickly nature. The black-tailed and antelope species of jackrabbit consume the cactus in times of drought because of the cactus' ability to store large amounts of water. Conversely, the collared peccary is happy to consume the prickly pear cactus even when other food sources are available.
Several species of bird eat parts of a cactus. The cactus wren eats the fruits and seeds of cacti in addition to its main diet, while the grasshopper sparrow will eat cactus seeds during the winter. Gambel's quails eat cacti if they come across them but do not actively seek them out and the curve-billed thrasher does the same with cactus fruits.
Numerous species of insect find cacti edible. The mealy bug infests the surface and root system of a cactus, while the scale insect attaches itself to the surface. The spider mite will also infest the surface of a cactus. The insects pierce the outer coating of the cactus and suck out the nutrients stored within, which can significantly harm the health of the cactus.
Not all cacti are edible by humans, but the "Opuntia" family of species are. These cacti, of which the prickly pear is a member, have both pads and fruit that can be eaten readily by humans. They are popular enough that the state fruit of Texas is the prickly pear.