Answer: Because they can only see the cacti in the day.
Fun Facts:
Cacti life circle lasts from 15 to 300 years, depending on the species.
Cacti come in very different sizes. One of the largest species can get 66 feet (20m) high and weigh up to 4800 pounds (2177kg) when fully loaded with water. Smallest species are usually just a few inches high.
Cacti are used to living in dry areas. Therefore, they can store a great amount of water and store it in stems and roots for surviving drought periods. Besides water storage, stems are also used for photosynthesis, a process of producing food from sunlight and carbon dioxide.
Roots of the cactus can reach up to 7 feet (2.1m) in diameter, although being just a few inches in the ground. The water is easily passed through the sand, so cacti are focused on low depth of the roots, but vide diametre, to gather as much water as they can.
Cacti have cylindrical, tree-like, rounded, starfish or irregular shapes. Their surface can be flat or covered in ridges.
The colors of cacti can be green, brown-green or blueish. On a surface, cactus produces a waxy substance, which prevents loss of water via transpiration (evaporating of the water through small holes during high-temperature periods).
