The Homeowners Column

The Homeowners Column

Good Bugs, Bad Bugs

Photo of Sandra Mason

Sandra Mason
Extension Educator, Horticulture
slmason@illinois.edu

As I was wandering around my yard on an El Nino winter day, my garden was certainly not in a January sleep. I could see the tips of a few spring flowering bulbs peeking through the mulch. Ladybugs were covering the leaves as an undulating red mass with black polka dots. As I admired my birch trees I noticed the egg masses of tent caterpillars. They look like a dark brown or grey collar encircling small twigs. A quick scratch with my thumbnail took care of that problem. I also noticed some egg cases of my resident praying mantids.

Around my house we see the Chinese egg case that looks like brown foam insulation about 2 inches long and often surrounding a plant stem. The smaller Carolina mantids have a 1 1/2 inch long case that looks like a brown zipper stuck to tree limbs or fences. The mantid egg cases I left.

During my wandering I had quickly made some decisions about good bugs, bad bugs and fun bugs to watch.

Lady bugs are good bugs. The adults and young larvae have voracious appetites for those bad guys - aphids. Tent caterpillars eat the leaves of fruit trees, birch and many other trees. Mantids are in the fascinating category and not really as helpful in controlling pests as some garden catalogs proclaim.

The young and adult mantids feed on just about any insect they can catch, including many beneficial insects, butterflies and each other. Mantids are nearly useless for pest control in home gardens because their diets are so diverse and they have poor survival rate.

Most of the mantids that hatch from an egg case will die from starvation or cannibalism. Mantids are territorial and by the end of the summer usually only one adult is left in the vicinity of the egg case...one big adult.

I know many people think the only good bug is a dead bug, but a very, very small percent of the insects and related species are actually harmful to us, our plants, structures or animals. Once you get past the "yuck" stage, insects are fascinating to watch. Insects have all the elements of a good science fiction movie. Plus they are in your own backyard and there is no admission fee, but you have to provide the popcorn.

Mantids may not be great pest control, but there are many unsung heroes of the bug world helping us out by eating or parasitizing the bad bugs. Some common beneficials are lady bugs, green lacewings, ground beetles, some flies and even some wasps.

Home gardeners should encourage naturally occurring beneficial insects by:

  • Learning how to recognize beneficial insects and common insect pests.

  • Reducing pesticide use and using specific pesticides such as Bt for caterpillars. Pesticides such as carbaryl (sold as Seven), rotenone and malathion can kill a variety of insects including beneficials. Be sure to identify the problem, analyze the situation or get professional assistance before using any pesticides.

  • Planting a variety of plants including flowers that can provide additional food (pollen and nectar). Sweet alyssum, yarrow, dill and fennel are good choices.

  • Providing overwintering areas for lady bugs by planting ground covers such as vinca or English ivy.

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