Ladybugs swarming your house? 'Tis the season.

Ladybugs swarming homes in Tennessee are the result of the 'perfect insect storm,' says one entomologist. Ladybugs typically take to swarming in autumn when temperatures start to drop.

Ladybugs swarming houses in autumn is not a new phenomenon. But this year's swarms of uninvited Coccinellidae family members are especially large in Tennessee.

"We have perfect weather conditions, and a large food population," David Cook, an entomologist and Davidson County Extension Agent, told Newschannel5.com in Nashville, Tenn. "This is a perfect insect storm."

Cook said that, as temperatures drop, the Asian Lady Beetles are simply looking for warmth and shelter. And they're especially drawn to light colored structures. In winter, ladybugs find places to ''hibernate." They've even been known to survive being frozen in blocks of ice. Their life span is about a year.

Of course, when the side of your house is suddenly blanketed by beetles, who crawl en masse into cracks and seep indoors, it can be disconcerting.

"There were probably one million of them," Diane Stroud of Lebanon, Tenn. told WTVF-TV.  "They were all over the porch, the far side of the house, everything was covered."

None of the 6,000 or so species of Coccinellidae family beetles found worldwide (including the 450 species in North America) are considered harmful to humans.

"It’s important to note that ladybugs are not structure-damaging pests – if touched or terrified, they can leave small stains as part of a defense reaction known as "reflex bleeding," which is intended to prevent predators from eating them. But they don’t enjoy meals of wood or fabric as other insects do – and I’ve never suffered a bite, although there some experts who swear they can land a well placed nip or two," writes Carrie Leber a garden blogger. 

Gardeners in the US tend to appreciate these beetles as beneficial because they eat aphids and other pests.  As the University of Floriday entomology department points out: "Many ladybird species are considered beneficial to humans because they eat phytophagous insects ("pests of plants", sometimes called "plant pests"), but not all eat pests of plants, and a few are themselves pests."

Some species of ladybugs eat mealybugs, some eat mites, and at least four species in Florida eat whiteflies. Some even dine on mildew.

In England, the Coccinellidae family of beetles has been named "ladybirds" for about six centuries. According to folklore, a village prayed to the Virgin Mary to stop a pest devouring their crops, and the red-jacketed beetle saved the day. After that, the beetle was called the "Bird of Our Lady." And "ladybird" somehow morphed into the common usage of "ladybug" in North America.

While there are some species of ladybugs whose populations are bulging (in Tennessee, for example), other native species of the beetle have become extremely rare.  The Lost Lady Bug Project is a Cornell University-National Science Foundation initiative aimed at documenting declining native ladybug populations by using pictures provided by volunteers (i.e. mostly school kids).  To date, almost 23,000 ladybug photos have been submitted, including some rare species, such as the two-spotted lady bug.

“This could be related to invasive species, habitat loss, pesticide use, or even simply the lack of people looking,” said Michelle Vedder, a Lost Lady Bug Project volunteer in Boston, to the Jamaica Plain Gazette. “The problem with all of these shifts is that we don’t how, or if, it is [affecting] the population of plant pests that ladybugs are so good at keeping in check.”