Why Do Ladybugs Swarm on Your House?
Why They Do It
Known as cluster-hibernators, ladybugs swarm because they're looking for a warm place to hibernate for winter.
When one of them finds a suitable place to spend the winter, it releases a pheromone that attracts a couple gazillion more of them. In fact, the pheromone can keep the ladybugs coming back year after year.
Not content to just sit there soakin' up the rays and workin' on their tans, they enter the house, often in large numbers. The kids don't have to stand there holding the door open, either.
Ladybugs simply find loose-fitting screens, cracks, and vents, and soon enough, they're house guests. It’s a phenomenon that causes a great deal of exasperation.
When And Where It Happens
This phenomenon happens every fall primarily from the Midwest to the eastern half of the U.S. and Canada. In southern New England where I’m from, it occurs on warm, sunny days in October and even into early November.
Ladybugs appear to be most attracted to houses with natural wood siding and ample southern exposure. They're also attracted to houses in wooded areas, light-colored houses warmed in sunlight, and especially older houses with lots of crevices.
While they are pests, they're not harmful to humans or pets, they don't reproduce during hibernation, and they don't damage structures.
Prevention Is The Best Solution
- To keep the bugs from getting in, repair loose-fitting windows and doors, seal cracks, and secure vents.
- If they get in, suck them up with a vacuum cleaner and release them outside, otherwise the survivors can crawl out of the bag and re-infest your house.
- Their bodily fluids are smelly and can stain, so avoid squishing or sweeping them.
- If you want to use an insecticide on them, select one that has pyrethrin as the active ingredient. Pyrethrin is a derivative of the chrysanthemum plant and is safer than permethrin, which is highly toxic to cats.
- In general, cats are more vulnerable to health problems caused by insecticides, so a call to your veterinarian would be a good idea before you start spraying indoors.
- Your veterinarian will want to know the active ingredient in the insecticide, and it's always listed on the can, often in the lower left section of the front of the can.
Interesting Facts About Ladybugs
- Ladybugs are a kind of beetle.
- Superstition has long held that they are a symbol of good luck and that killing one is bad luck. My hunch is that this superstition has resulted in far more ladybug lives being saved than episodes of good fortune.
- There are some 400 species of ladybugs in the U.S., and most of them are beneficial.
- Worldwide, there are over 40,000 different species of beetles.
- Ladybugs are voracious predators, consuming aphids and other insects that are harmful to plants. That's the silver lining in this cloud of ladybugs. If you have houseplants, it may behoove you to become a ladybug rancher.
A Beetle Similar To The Lady Beetle May Also Swarm On Your House
There's another species of beetle that will probably swarm your property and that you're likely to confuse with the lady beetle; the multicolored Asian lady beetle, pictured below. It, too, is beneficial.
Here's How To Tell Them Apart
- Its color ranges from yellow to yellowish-orange
- It has a bunch of black spots on the dome-like shell that covers most of its body.
- 19 is the maximum number of spots you'll find on the Asian lady beetle.
- The pronotum, that collar-like area between the head and wings, features a marking that resembles a black capital M.
How The Asian Lady Beetle Got Here
The United States Department of Agriculture (USDA) released the Asian lady beetle in Georgia and other southern states between 1978 and 1982 as a natural control for pest insects.
But that bunch vanished and no others were seen until 1988, when they showed up in Louisiana, apparent stow-aways on a ship docked in New Orleans. Now they're found all over the eastern U.S. and eastern Canada.
An Educational And Environmentally-Friendly Alternative Solution
You can build or buy lady bug houses in which the insects can hibernate. These houses can be purchased online and at wild bird specialty stores, nature or science stores, feed and grain stores, and, I'll bet, in museum and zoo gift shops, and Audubon Wildlife Sanctuaries. You can also find plans online so you can build your own lady bug house.
Questions & Answers
© 2012 Bob Bamberg