Heaps of ladybugs recently turned branches, leaves and patches of trees along a Santa Monica Mountains trail into a moving jumble of red wings and tiny black dots. A cold spell may be the reason for the pileup, said Ileene Anderson, a senior scientist with the Center for Biological Diversity. “They don’t produce their own body heat,” she said. “So, they group together to try to stay warm. Also, it helps in finding mates.” Anderson, based in Los Angeles, said the phenomenon isn’t unusual. People spot the masses of ladybugs – called aggregations – often during cold times of the year.