Lady beetles, commonly called ladybugs, usually aggregate in groups over the winter. Normally they congregate in leaf litter, tree cavities, house vents, attics, garages, sheds, and firewood piles. However, for at least three years Asian spotted lady beetles (Harmonia axyridis) have been overwintering in UC Master Gardener Ted Hawkins's outdoors pickup truck! They apparently crawl into a crack of a truck door, assembling in the compartment behind the panel. They gather in both the driver and passenger doors, going back and forth between the two doors. However, they seem to spend more time in the passenger door, presumably because it is used less and thus are disturbed less.
Overwintering
Ted Hawkins pointing to the ladybugs overwintering in his truck.
Most lady beetles eat insects (aphids are a common food source), which generally disappear during the cold winter months. Overwintering lady beetles go into diapause where their metabolism slows down, reducing the need for food and water. Diapause also enables them to utilize supercooling where the water in their bodies can cool down below the freezing point of 32°F/0°C without forming ice crystals, which would cause their bodies to freeze.
Once a ladybug has found an ideal location to spend the winter, it will release species-specific pheromones to call other ladybugs to the area. By congregating together with hundreds of other ladybugs they gain some protection from the cold and reduce opportunities for potential predators to consume them while they are in a dormant state.
Unlike some troublesome pests that can occupy areas in and around your home, such as spiders, moths or ants, overwintering ladybugs are mostly a charming nuisance.
Ending Diapause
ladybugs in Ted's truck
Lady beetles will come out of diapause when the weather begins to warm up in the spring around 55°F/13°C. The insects that they feed upon return during this time as well.
The lady beetles in Ted's truck have been arriving sometime in late autumn as the weather cools down and remain there until spring when the temperatures warm up. Ted has enjoyed having the lady beetles take residence in his truck during these past few years and hopes they will be back this fall. Hopefully, as they depart his pickup doors this spring, they will eat any aphids that may be in his garden before moving on, as a “thank you” for giving them winter shelter.
