Ladybugs: are they beneficial? Invasive? I know that nurseries sell them for release into the garden. Is that a good idea?
The type of ladybug most often for sale is an introduced species. This factsheet from Linda Chalker-Scott of Washington State University provides a thorough explanation of why it is problematic.
Multicolored Asian lady beetles are generalist predators and they can be beneficial in the garden, but they also displace the North American native species of lady beetle. Purchasing them is not recommended and is probably a waste of money because, well, they have wings, and they will fly away. Former University of Washington Botanic Gardens director Sarah Reichard’s book, The Conscientious Gardener, advises that you instead avoid using insecticides so that your landscape will naturally attract beneficial insects, particularly native ones.
Another drawback of releasing ladybug larvae in your garden is that they sometimes find their way indoors, where you don’t want them to be. The multicolored Asian lady beetles (Harmonia axyridis) look for crevices to spend the winter hibernating and they seem particularly fond of light colored south walls. If you don’t want to find thousands of these beneficial insects flying around your house on the first sunny day in spring, fill the cracks in your house siding with caulk. For a description, management ideas, and detailed vacuum cleaner bagging instructions, Ohio State University Extension has a fact sheet on these insects. Inside a home, the insect droppings are a human health hazard, and can trigger asthma and other allergic reactions.