Monarch butterfly overwintering colonies in Mexico face threats from illegal logging, climate disruption, and extreme weather that cause mass mortality events.
Monarchs in overwintering colonies disturbed by extreme weather or premature temperature increases expend critical fat reserves in out-of-season flight and activity. Cold, wet conditions penetrate their dense wing-covering clusters, causing death from hypothermia that can kill hundreds of millions of individuals in a single storm event. The disruption of the microclimate within intact forest by logging reduces the thermal buffering that protects overwintering colonies from temperature extremes. The welfare significance of such events depends on insect sentience debates, but the scale of mortality - potentially hundreds of millions of individuals in a single event - merits serious consideration regardless of where those debates settle.