- "It happens again and again. The Wraith allow our kind to grow in numbers, and when that number reaches a certain point they return to cull their human herd."
- —Teyla Emmagan
Cullings occur in a variety of ways and can range greatly in severity. During the periods of extended hibernation that occur in Wraith society, the scope of cullings is generally small. These culling may only consist of a handful of Wraith Darts that arrive via Stargate. During such events, only a handful of people are generally taken and the damage to a planet's infrastructure is minimal. These cullings largely only serve to remind the Human populations of the Pegasus galaxy of the persistent Wraith presence, and to instill fear among them. (ATL: "Rising", "The Pegasus Project", "Underground")
Between periods of hybernation, however, Cullings may be much more severe. During full-scale cullings, Hive ships and cruisers are utilized - arriving in orbit and deploying waves of darts to the planet below. These cullings can devastate entire civilizations in terms of the number of people taken and the sheer destruction caused by weapons fire from the atmosphere. (ATL: "Letters from Pegasus", "The Hive") Ground forces are usually also deployed in order to locate any who may be hiding. (ATL: "Outsiders") In some instances, the Wraith dial in to the planet's Stargate in order to prevent escape. When the culling is over, these forces then return to the Hive Ships, where the captured humans are placed in cocoons to preserve them for later feedings. However, despite the severity of the cullings, the Wraith always leave behind survivors that will be able to repopulate the planet, and therefore be able to replenish the Wraith's food supply.
Once the Wraith have culled a sufficient number of worlds as to adequately replenish their society, they enter a period of hibernation that can last up to 50 years. During this time, Hive ships land on planets, individual wraith enter hibernation pods, and only a handful of 'caretakers' are left behind to maintain the society. (ATL: "Rising")
Races including the Satedans, Athosians, and countless others have faced almost complete destruction from such events. Because of the unpredictable nature of such cullings, and the limited technological advancement of most Pegasus-galaxy cultures, little can usually be done to prepare for a culling. This has caused several societies to take what few precautions they can. To this end, the Hoffans constructed massive archives hidden throughout their planet in order to ensure that Hoffan history and knowledge wouldn't be lost for the remaining survivors left to rebuild. (ATL: "Poisoning the Well")
The Genii built entire sub-terranian cities in order to advance technologically while not attracting the attention of the wraith. This has enabled them to make such advances as projectile and atomic weaponry, making them among the few societies in the Pegasus galaxy capable of 'effectively' resisting the wraith. (ATL: "Underground", "The Return, Part 1") The Travelers travel the galaxy in generational ships in order to evade being culled. (ATL: "Travelers") Many other races simply hide in order to avoid attack. (ATL: "Travelers", "The Lost Tribe", "Ghost in the Machine")
The Atlantis expedition has worked towards creating a 'treatment' that would allow Wraith to receive nourishment from 'real food', thus eliminating the need to feed on humans and cull planets. However, initial tests proved unsuccessful. Furthermore, the act of culling and feeding has become such a core part of Wraith society that receiving sustenance from any other method would be a radical change that many wraith would be wary of. (ATL: "Infection", "The Queen")