Cacnea are not true desert pokemon, for although they can store water within themselves for a month, they can not absorb a month's water from desert rains. Every month, on the night of the new moon, the Cacnea wander from the desert to the nearest lake, sea, or reservoir to drink en masse, drinking smaller bodies of water nearly dry – a practice which saw them once hated as pests, but in time people came to depend on the Cacnea march in order to prevent flooding.
The reason Cacnea choose to live in deserts is because when veiled within sandstorms, Cacnea can create elaborate mirages by instantly growing large flowers from their head and shooting their spikes into the air at angles where sandstorms can keep them aloft. They do not display these mirages at planned shows, but spontaneously, and continue for hours while weary travelers and local pokemon alike gather to watch. Taking advantage of their ability to store water, Cacnea often remove a few water-filled spikes with which to provide refreshments, at times combined with fruits from their flowers and meat slain in battle. Many have speculated that it is this water, not their performance, which truly draws people to their shows, an accusation which has shattered many a Cacnea's pride.
Yet some offer a much prouder explanation. The fossil record shows Cacnea to be the oldest desert pokemon, older than even Lileep and Anorith. Most speculate that they formed the base of the original desert food chain, and only later developed venom which made them inedible. Yet there is a good deal of evidence to suggest instead that life in the desert began only when other pokemon migrated to follow the mirages; that the Cacnea's refreshments, not their bodies, were the original desert food.