Extension Educator, Horticulture
They're back! Actually they never really left. Asian lady beetles have just been preoccupied with eating soybean aphids all summer. Just like the hound chasing the fox the migration of the soybean aphids (you know those recent pesky clouds of bugs) translates into the migration of their predator. As their food source declines in the fields, Asian lady beetles start searching for a new fast food joint and a winter retreat.
Lady beetles are considered good bugs. They eat lots of pest species like aphids and scale. Both the young larva and the adults feed on a wide range of insects. Multicolored Asian ladybeetles are very good at controlling aphids on trees and shrubs. They were first imported into Georgia to control the pecan aphid. Even though there are several species of beneficial native lady beetles in Illinois, this exotic lady is giving the rest a bad name.
The multicolored Asian lady beetles are one-fourth inch long and are the VW bug dome shape. They usually have orange wingcovers with 19 black spots. No need to count. Their multicolored name comes from the variety of color possibilities ranging from tan to red and the spots may be very small to absent, to large and obvious. As they are biting your arm, you can also see four black spots behind the head that forms a "W" when viewed from the front or an "M" when viewed from behind.
Asian lady beetles like to taste things including us. They can and do bite in order to discover our fitness as a meal. Although they have no venom, the bite hurts and can leave a red mark. They can also eat divots out of apples, grapes and raspberries.
In their native areas in Asia these lady beetles spend the winter in cracks and crevices of cliffs. Cliffs are tough to find in central Illinois. What's the next best upright thing around?…… Our buildings of course. In the fall they start their migration flights. They are particularly attracted to light colored structures with sunny exposures. They congregate in large herds on the sides of buildings. They wander around and enter buildings through cracks between siding, around windows, around roof flashing and overhangs. Or they may fly through opened doors.
If buildings are unheated, the beetles just snuggle together and wait for spring. In heated buildings especially on bright sunny days they may start flying around trying to escape. These eventually die on the windowsill.
The good news is ladybugs don't reproduce or feed while they are indoors. Controlling these insects indoors consists of vacuuming (be sure to empty the bag afterwards) or your best scoop and toss outside method. Forget foggers or aerosol sprays. Don't smash them on furniture or drapes since they can leave a stain. If crushed, the beetles emit a foul odor. Soon they will all have gone outside one way or the other.
Insecticide sprays provide limited help. You may get some satisfaction out of spraying insecticidal soap every couple days outdoors on congregation walls and then throwing the bottle at them. Outdoor foundation sprays of residual pyrethroid insecticides containing active ingredients such as bifenthrin or permethrin may be helpful if sprayed now before beetles find a way indoors.
Preventing ladybeetles from entering buildings is the best control measure. Caulking cracks and crevices around windows, along the foundation and around doors will help reduce the numbers wandering indoors.
Commercially available indoor black light traps can be useful in heated storage buildings or garages. However the traps are effective only at night and best used in rooms without other lights.
Remember outdoors ladybugs are good bugs. Repeat this over and over to yourself as you are scooping them up from your windowsills. A useful UI fact sheet http://www.ipm.uiuc.edu/hyg/insects/asian_lady_beetle/index.html