Good bugs in the garden

Most may not realize that over 97 percent of insects, spiders, and similar bugs (better known as “arthropods”) in home gardens and landscapes are beneficial. That is, they either do no harm, provide food for desirable species such as birds, or prey upon insects we consider bad and destructive to our crops. Knowing some of the most common good bugs, and how to help and not harm them, will help minimize pest problems and the use of pesticides.

There are two main groups of beneficial insects. The predators, such as spiders and lady beetles, are generally larger than their prey, killing and feeding on them. The parasitoids, such as parasitic wasps and flies, are generally smaller than their hosts and lay eggs on or within them. When these eggs hatch, the resulting larvae (like small caterpillars) kill the host insects by feeding on them.

A University of Maine Extension bulletin provides ten tips to attract and sustain these beneficial insects.

*Develop a tolerance to some damage to your plants. Most plants tolerate low levels with no lasting harm.

*Provide shelter for your good bugs from adverse weather such as extreme heat. This just might be leaf litter and debris under shrubs (don’t be too tidy around them).

*Increase the diversity of plantings in your landscape. A wide range of plants will support a wide range of beneficial insects. Avoiding monoculture with only one species of plant ensures that if you do get a problem, it wont get out of control and wipe your plantings out.

*Don’t use bug zapper lights, those bluish ones that attract insects with ultraviolet light, then electrocute them. A University of Delaware study found these lights kill mainly harmless insects and not biting flies. In fact, most mosquito species are not attracted to ultraviolet light.

*Think before you spray. This often kills beneficial insects as well as bad ones. Cutting out webworm nests from trees, picking off Japanese beetles, and improving airflow to deter slugs are examples of simple, non-toxic physical controls.

*Regularly inspect plants for pests. It is much easier to control them as they just appear.

*Know your insects before you make a decision on whether to control. Extension services, garden stores with trained staff, books, and online websites are useful in identification.

*Provide plants for predators. These include flowers with umbels (umbrella-like clusters) such as yarrow, composites such as daisies, spikes such as lavender and goldenrod, and flat cups such as buttercups. Many predators like what we don’t and call weeds. It may be helpful to have a nearby patch for such “wildflowers.”

*Keep plants healthy. Pests usually attack weakened or stressed plants. These stresses can be created by improper watering (too much as well as too little in a drought, or sandy soil), improper placement of plants according to light and soil needs, mulching too close and deep around plants, and improper fertilization. Too much fertilizer, especially nitrogen, may be worse than too little. Lush plants from excess fertilizer are favorite targets for pests such as aphids, mites, and the black vine weevil.

*In addition to the above tips concerning managing your yard or garden for beneficial insects, some consider buying and bringing more in. These can be purchased from specialty catalogs and websites. Importing beneficials can be complex in order to have success. You must determine the proper beneficial, best time to release it for the life cycle of the pest, how many are needed, and proper release requirements such as time of day, food, and water needs. Use of imported beneficials is much easier in a greenhouse, as often outdoors they fly away.

Dr. Leonard Perry is Extension Professor, Department of Plant and Soil Science at the University of Vermont. Visit his website at