Most of the beetles travel 50 miles or more into the Sierra Nevada. Significant numbers of them also drift into the Coast Ranges to winter in places such as Uvas Canyon. Most of the beetles do not find aphids in the mountains, so they feed on pollen. Heavy with fat from the pollen, they bed down in leaf litter for what amounts to a nine-month period of lethargy. October rains may cause the ladybugs to briefly stir, but only to move farther away from streams.
Entomologists can only guess at why the beetles crowd together.
One theory suggests that the aggregations may be vital to female ladybugs securing many mates. A clear, bright day in February will trigger the clusters to break apart. The air is so thick with them during this time, say the rangers at Uvas, they'll stick on your clothes. Soon after mating, the ladybugs of Uvas Canyon rise high into the atmosphere. The same phenomenon also occurs in other parts of the Coast Range and the Sierra Nevada.