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GardenSMART :: Lady Bugs: Friend or Foe?

Lady Bugs: Friend or Foe?

By Steve Kuhse, B.C.E., Service Quality Manager, Entomology and Regulatory Services, Terminix
Photos courtesy of Terminix

If you’re like me growing up, lady bugs were right up there with butterflies and lighting bugs as some of the coolest critters on earth. Like many other species of plants and animals, there are however different species of lady bugs, or more properly called lady beetles, that share our world.  

The Asian Multicolored Lady Beetle, Harmonia axyridis was introduced into the United States from Asia from 1978 to 1981 to control aphids, scale, and other crop pests. They have since adapted quite well and are now widely distributed east of the Mississippi River, and have been documented in areas of the Midwest, Southwest and Pacific Northwest. Other native lady beetle species that may be found around the home are the convergent lady beetle, Hippodamia convergens and Australian lady beetle, Rodolia cardinalis, which is native to California.

Asian lady beetle adults are slightly larger than native species and have the key identifying feature of two white, oval markings on the shield over the thorax bordering a dark M-shaped marking.

Though both immature and adult Asian lady beetles are helpful to us outside as voracious feeders on plant pests, they have adapted to buildings as a preferred overwintering harborage causing them to become a significant structural pest. Like other lady beetles, these insects respond to handling by emitting a foul smelling, yellow fluid which is known to stain fabrics of draperies and upholstered furniture on which the beetle may be crawling when disturbed. There also have been verified reports of beetles landing on humans and gnawing to the point of discomfort, along with causing damage to fruit crops.

Asian lady beetles enter our homes and businesses during cool evenings in the late summer and early fall, which signals the approach of winter and triggers their overwintering site-selection behavior. At this time of year the sun heats the west and south walls of the building, which attracts lady beetles, often in large numbers, over a period of weeks. Any opening that permits access to voids behind exterior walls may be used, especially around windows and doors, soffits, weep holes, and beneath exterior wall coverings. Since these insects can fly, the upper floors or attics are a common entry point through roof-line gaps or poorly screened vents.

Once inside walls lady beetles crawl as far as they can until selecting a site to settle into their overwintering, quiescent state. When warm winter days occur they awaken and generally crawl towards the warmest areas, usually through recessed lights, ventilation openings and other fixtures into living spaces.

Asian lady beetles are best controlled through preventative efforts. Once they are inside walls and other voids, total control is nearly impossible as location and access to all infested areas is difficult.  For any structure with a prior history of problems, the Pest Management Professional or building owner should take steps during the summer to find and seal as many exterior entry points as possible, concentrating on the south and west walls. Caulking window and door frames, and ensuring that foundation and attic vents are tightly screened will help to prevent lady beetle entry.

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