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The pesky box elder bug is usually attracted to the female box elder tree.

Garden dectective: Box elder bugs

Published: Saturday, Jul. 28, 2012 - 12:00 am | Page 9CALIFORNIA LIFE
Last Modified: Saturday, Jul. 28, 2012 - 6:09 pm

Our deck is inundated with box elder bugs. We got some Ortho spray at the nursery that says it kills box elder bugs. We sprayed the screen door and put little lids around the edge with poison in them.

We seem to have fewer around the door where we sprayed, but they crawl all over the tomato plants and fly all over the deck. And they crawl on us.

Any better solution?

– L. Rittenhouse, Fair Oaks

According to UC master gardener Debbie Rogenmoser, the box elder bug when full grown is about a half-inch long and one-third as wide.

Adults are mostly black and have three red lines on the body and several fine red lines on each wing. The wings lie flat on the insect's back when it is at rest. The abdomen is red.

As you have discovered, the box elder bug can be an annoying pest around and in homes. Box elder bugs usually feed on the leaves, flowers and seed pods of the female or seed-bearing box elder tree (Acer negundo). They may also subsist on male box elder trees and occasionally occur on maple and ash trees.

Large numbers of the bugs usually occur only on female box elder trees. Removing the trees is the most effective control; however, these insects can fly several blocks.

They are not harmful to people or pets, but when they come indoors, they can be annoying and may spot curtains, furnishings and clothing with their excrement.

When crushed, they give off an offensive odor. They do not breed indoors. If trapped indoors, they will eventually die.

The first step in managing infestations is to remove any fallen seeds from beneath the trees and around your yard. A shop vacuum will remove most seeds from grassy areas. Eliminate hiding places such as rocks, boards, etc.

Try to maintain a weed- and grass-free strip, 6 to 10 feet wide, around the home's foundation, especially on the south and west sides.

Finally, you can wash box elder bugs off walls or tree trunks with a forceful stream of water from a hose.

Repair torn screens and close up places where the bugs can enter the house, such as cracks around doors and windows, and attic or basement vents.

Box elder bugs that enter the home may be controlled by hand-collecting or vacuuming.

Your best defense is to deny box elder bugs a place to live and hide in your yard. Chemical controls are often no more effective than vacuuming and hosing, and repeated applications may be required. Insecticidal soap applied in a forceful spray of water may reduce populations on tree trunks.

Pyrethroid insecticides are available for treating foundation walls around the perimeter of buildings, but these are best applied by a professional. Special care must be taken to avoid runoff of pesticides into storm drains, because they lead to creeks and rivers. Do not use sprays for box elder bugs inside the house.

More information is available online at


Questions are answered by master gardeners at the UC Cooperative Extension services in Sacramento and Placer counties.

Send questions to Garden Detective, P.O. Box 15779, Sacramento, CA 95852. Send email to h& Please put "Garden Detective" in the subject field and include your postal address.

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