The prickly pear cactus (plant on the left) is common in the Sacromonte. The shallow root system enables the plant to grow in shallow, loose soils, which are common on the slopes of the Sacromonte. It can also tolerate long periods without water and occasional frosts.
The fruit of prickly pears, commonly called cactus fruit, cactus fig, or tuna in Spanish, is edible, although it must be peeled carefully to remove the small spines on the outer skin before consumption. It is not uncommon to see gypsies selling prickly pears in Granada. They wear thick washing up gloves to protect their hands from the spines. They completely cut off the skin before selling the fruit. The spines of prickly pears can easily get stuck in the skin and they can break off and become embedded. If you pick up a prickly pear with your bare hands the spines will itch and be uncomfortable for several days afterwards. (I have personal experience)
In Australia, prickly pears became a widespread invasive weed, eventually converting 260,000 km2 of farming land into an impenetrable green jungle, in places over 6 metres high.
A lot of the prickly pear in the Sacromonte and other places near Granada are covered in, what looks like, a grey substance. This is actually is an insect from which cochineal dye is derived. This insect, lives on cacti, feeding on moisture and nutrients in the cactus sap. The insect produces carminic acid, which deters predation by other insects. The carminic acid can be extracted from the insect's body and eggs to make the red dye. If you scrape a little of the grey matter with you finger and then wipe it on another surface you will see the deep red colour.
Prickly pear is often used as a type of fence to deter intruders into a garden or a cave. The spikes and spines have a big deterrent effect for anyone who wants to pass through a prickly pear thicket. In the autumn of 1961, Cuba had its troops plant an 13 km barrier of prickly pear cactus along fence surrounding the Guantanamo Bay Naval Base to stop Cubans from escaping Cuba. This was dubbed the "Cactus Curtain", an allusion to Europe's Iron Curtain.