Large numbers of lady beetles generally begin to fly to buildings on the second day of temperatures above 65 degrees F that follow freezing or near freezing temperatures.
Once lady beetles reach buildings, they crawl into cracks and gaps around windows, doors, roof lines, and other openings. Some continue to move inside the structure until they reach the living areas of homes where they soon die. Others will find suitable overwintering inside wall voids, attics, and other areas. Mild, sunny winter days can wake these dormant insects. The warmth will reach them at different rates, depending on where the lady beetles are located within the building, so they do not all become active at the same time. As they wake up, they follow the warmth into the home's living quarters. Once there, they move towards windows and other sunny areas. Eventually all lady beetles overwintering inside buildings become active. During spring, they try to move outdoors but many remain trapped indoors. Although multicolored Asian lady beetles can be a nuisance when they occur in large numbers, they do not infest wood, destroy fabrics, eat our food, or damage other property. These lady beetles cannot sting and they are not known to carry disease. They do not reproduce indoors---they entered in the fall.
However, there are some problems with multicolored Asian lady beetles. First, some can bite hard enough to break human skin, causing minor, short-lived discomfort. These bites are incidental, as the beetles are presumably searching for moisture or food. Second, they can secrete a strong-smelling yellowish liquid from the joints of their legs, a process called reflex bleeding. This liquid can stain light colored surfaces. Third, exposure to dead lady beetles in buildings can cause allergic reactions in a small number of individuals.
Prevention is the most effective step in managing lady beetles. Check the outside of your home for spaces and cracks that may allow insects easy entry. Lady beetles can fit through openings as small as 1/8 inch in size. Make any necessary repairs by the end of September. This will not eliminate all lady beetles but it can significantly reduce the number entering buildings.
- Seal cracks and spaces around doors, windows and fascia boards. Also check for gaps and cracks where different materials meet, such as brick and wood siding. Seal cracks with caulk, such as silicone, elastomeric latex, or silicone/acrylic.
- Seal areas where cable TV wires, phone lines, and other utility wires and pipes, outdoor facets, dryer vents and similar objects enter buildings. Seal with caulk or for larger spaces use polyurethane expandable spray foam, steel wool, copper mesh, or other appropriate sealant.
- Repair or replace damaged window and door screens. Repair or replace damaged screens in roof and soffit vents, and in bathroom and kitchen fans.
- Install door sweeps or thresholds to all exterior entry doors. Install a rubber seal along the bottom of garage doors
Physical exclusion can be supplemented with a residual insecticide barrier. For insecticides to be effective, they must be applied before insects begin to enter buildings. The best time to treat is usually late September or early October. Some examples of effective insecticides available to the public include those containing:
CAUTION: Read all label directions carefully before buying insecticides and again before applying them. Information on the label should be used as the final authority.
Be sure the product you intend to use is labeled for use on the exterior of buildings. Apply the insecticide according to label directions around doors, windows, and roof lines, paying particular attention to the south and west sides where the insects are most numerous. You may also consider hiring a structural pest management service. Pest management professionals have experience as well as access to additional residual insecticides for effectively managing lady beetles. Good luck!