Some of a gardener's best friends are bugs. Yes, bugs. Many of the insects and other creepy-crawlies in our flower beds and vegetable patches and on trees are doing good work. Most are harmless, though there are a few that might do our plants significant harm.
Some beneficial or helpful insects are pollinators, carrying pollen from male to female plant parts to fertilize flowers so they can develop fruit or seeds, says Stephanie Adams, plant health care research specialist at The Morton Arboretum in Lisle, where Dave Rogers' Big Bugs exhibition of outsize sculptures has just opened. Without pollinators like bees and moths, we would have no tomatoes or cotton.
Other helpful insects are hunters, such as praying mantises, spiders and ladybugs. Yes, that cute polka-dotted red ladybug is a meat-eater, a predator of aphids. Fireflies are hunters too, when they are larvae, before they enter their flashy flying beetle stage. Many beetles and insect larvae are gardener-friendly predators of plant pests.
And all the things that crawl and burrow in the ground, including larvae, centipedes and earthworms, also benefit plants by aerating the soil, Adams says.
One threat to this lively, helpful army of insect friends comes from pesticides. If you spray insecticides carelessly, you risk killing beneficial insects as well as harmful ones. A chemical may not work at all if it is the wrong insecticide for your target insect, or if the insect is not at a vulnerable stage in its life cycle. "Sometimes you accidentally kill the predators and then the pests will flourish, because there is nothing to keep them in check," Adams says. Improper use of chemicals also can lead pests to develop resistance, making the pesticides less effective.
If you fear a bug is harming your plants, "Identification is paramount," Adams says. Before you apply any chemicals, bring a sample of the insect for a solid identification to a good garden center or a source like the Arboretum's Plant Clinic (630-719-2424 or email@example.com). Get advice on how you might handle the problem without chemicals. If you decide to spray, choose the right chemical and follow the label directions precisely.
Beth Botts is a staff writer at The Morton Arboretum in Lisle (mortonarb.org).