The good, and bad, of the bug world

June 03, 2008|By ANNETTE IPSAN

As spring swings toward summer, a new bevy of bugs arrives, some with good news and some with bad news. Armed with information and insight, you can stop harmful insects in their tracks and encourage the good guys. The trick lies in knowing the difference. Bagworms and carpenter bees illustrate well the good and the bad among bugs.

Battling bothersome bagworms

"The pinecones on my tree are moving!" This startled statement often heralds a chat about bagworms.

A serious pest of trees and shrubs, bagworms aren't worms at all, but the larva of a moth. Their claim to fame is the spiny oval bag they make and tote with them as they feed. It's made from bits of leaves or needles and looks like a tiny pinecone.

Bagworms have good appetites, chewing the leaves off many evergreens and deciduous trees. Conifers such as arborvitae, cedars, junipers and pines are favorites. But, they will eagerly attack maples, locust, linden and many other trees that lose their leaves.


Bagworm eggs hatch around the first week in June. The tiny larva start munching on leaves right away and spinning web and bits of the plant into their bags. Look for the tiny larva and bags on favored trees and remove and destroy them.

By August or September, the bags - and the bagworms - are an inch or two long. At this point, the bagworms fasten their bags to a branch with silk, pupate and emerge as moths. The males fly, but the females stay tucked in their bags, laying 200 to 1,000 eggs.

You want to stop the process much earlier to prevent damage. Mid-June to mid-July is the best time to spray BT (Bacillus thuriengiensis), a naturally occurring bacteria that kills small caterpillars but doesn't harm people or pets. You'll find BT in better garden centers under names like Dipel or Thuricide.

If you just have a few bagworms and no major damage, you can control them by handpicking and destroying their bags in the fall and winter. Since each bag can contain hundreds of eggs, this can be very effective. I've controlled several minor outbreaks on my Hinoki cypress and Colorado spruce with this method.

Coping with carpenter bees

"Bumblebees are destroying my deck!" This cry cues a discussion of bees.

Both bumblebees and carpenter bees are good pollinators, feeding on pollen and nectar. Both have large, fuzzy black and yellow bodies. Carpenter bees, however, have shiny abdomens and love to bore holes in wood.

Well-named, carpenter bees bore neat one-half inch holes into unfinished wood on decks, porches, garages and trim. They then lay eggs in these tunnels.

Male carpenter bees guard the nest, buzzing around it and chasing off interloping bees. Their guarding behavior is often misinterpreted as aggression by people sipping lemonade on their decks. But, carpenter bees rarely sting. Females are docile and males have no stingers.

Finished wood structures are your best defense against damage by carpenter bees. Raw, unsealed or weathered wood invites tunneling as does nail holes, cracks, splinters or exposed saw cuts. So, paint or seal exposed wood.

If you already have carpenter bee tunnels, treat them with an insecticide. Spray the tunnel entrance with a wasp, hornet and bee spray. Or, puff Carbaryl insecticide dust into the tunnel. Wait a week, then seal the hole with a deep plug of wood putty.

Remember, carpenter bees are good pollinators. If you do your part and seal all of your outdoor wood surfaces, they will do no damage and continue their vital role in keeping flowers blooming and fruits and vegetables producing.

The good bug/bad bug story continues throughout the seasons, giving you many opportunities to give a helping hand to the good guys and deal firmly with the bad guys. Before you squish or spray, give me a call and I'll tell you if your bug helps or harms. Then I'll share ways you can protect beneficial insects and discourage damaging ones.

Annette Ipsan is the extension educator for horticulture and the Master Gardener program in Washington County for the University of Maryland Cooperative Extension. She can be reached weekdays by telephone at 301-791-1604 or by e-mail at

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