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On the day after Thanksgiving my Dad and I hiked up the Nelson Trail that follows the
Tule River just east of Camp Nelson.  We were surprised to find oodles of ladybugs in
several locations along the trail.  I had heard about this phenomenon of hibernating
ladybugs but hadn't seen it myself until then.  It seems that for nine months or so out of
the year there are huge clusters of hibernating ladybugs gathered on fallen trees and in
shrubs in the coast ranges and the foothills of the Sierra Neveda.  They tend to be in
open areas where the sun shines through the trees.  Laboratory experiments suggest
that the clustering is stimulated by reduced temperatures and less light. In the Sierra
ladybugs have been found as high as 6,000 feet clustering and surviving under snow
drifts! The ladybugs are basically hibernating and do not eat but live off their
accumulated aphid fat.

Why the huge clusters? One suggestion is that predators (birds) are discouraged from
eating ladybugs because of the obnoxious odors emitted by the large group. But another
major motivating factor may be for mating...
Hibernating ladybugs along the Nelson Trail
Giant Sequoia National Monument