Balancing the Bugs

Learn about the good, the bad and the downright creepy to keep your garden safe and thriving.

| May/June 2008

orange assassin bug

An orange assassin bug waits for prey.

Did you know that close to a thousand species of insects live in your yard? Good ones and bad, functioning together in a carefully balanced ecosystem. As responsible keepers of our planet, we continually need to make decisions about how to live with both. What follows is not intended as instruction for controlling those invertebrates, but rather a guide to using nature’s ways to maintain the balance.

Whether you call them “insects” or “bugs” (which in some taxonomies are actually a subgroup of insects), of the nearly 100,000 known species, only 600 are considered to be pests. Do you know which are which?

Finding the good guys

Most beneficial insects are pollinators, predators or parasites. Pollinating insects move pollen between bisexual plants, or within unisexual plants, thereby guaranteeing reproduction. Bees and butterflies are pollinators. Predatory insects eat other insects; spiders immediately come to mind, but they aren’t insects, they’re arachnids. The assassin bug (Reduviidae sp.) is a good example of a predatory insect; fly-eating wasps fall into this category, too. Parasitic insects are really parasitoids because they invariably kill their host. So-called parasitic wasps are included in this category because their larval form lives in, and ultimately consumes, its host. Keeping your landscape healthy requires the presence of these good guys to keep things in balance. If you use insecticides to eradicate the pests, you run the risk of killing the beneficial insects directly, and you destroy the food source for some of them as well.

Beneficials of note

One of the most voracious predatory insects is the convergent ladybird beetle (Hippodamia convergens), commonly called a “ladybug.” This species consumes huge quantities of aphids, scale insects and mites and is sold commercially for agricultural pest control. Identifying features include two to 13 black spots on red wing covers and a distinctive black and white pattern behind the head. This diminutive insect is not to be confused with the invasive multicolored Asian ladybeetle (Harmonia axyridis), an annoying pest that invades our homes in the fall, littering windowsills and clogging vacuum cleaners. Asian ladybeetles range in color from yellow to orange to red, with up to 19 spots or none – their thorax (body segment behind the head) is also partially white or cream colored. Despite their bad rap-sheet, Asian ladybeetles consume copious quantities of scale insects and aphids, and are responsible for benefiting the pecan industry significantly by eliminating the pecan aphid as well as other insect pests in fruit orchards, tree farms and agricultural crops.

Another insect worth inviting to your garden is the praying mantis (Mantidae). These Transformer-like creatures are a little spooky at mature size (up to 5 inches), but harmless to humans and quite intriguing to watch. Mantids consume many insects, but unfortunately, they are not discriminating and will snare anything that gets close, including butterflies, honeybees, small frogs, snakes and their own kind. The Carolina mantis (Stagmomantis carolina) is the smallest of the group and native to the United States; two imported mantids are also found in most parts of the country – the European mantis (Mantis religiosa) and the Chinese mantis (Tenodera aridifolia), which is also the largest. Chinese mantis egg cases (oothecae) are often sold commercially for biological insect control, but if you look carefully in the fall, you’ll probably find one or two hidden in ornamental grasses or thick shrubs.

Other beneficial insects commonly found in the landscape include all bee-type insects that pollinate flowers, including the aggressive-but-harmless carpenter bee (Xylocopa virginica). Dragonflies are well-known for their diligent pursuit of dinner. Watch for a dragonfly swooping back and forth through your garden; it’s catching hundreds of mosquitoes, midges, gnats and flies. Brilliant green katydids (Amblycorypha longinicta) look very much like grasshoppers. They will occasionally munch on leaves or flower petals, but many of them are predatory and will eat grasshoppers and other destructive insects. Also included in the beneficial insect division are lacewings (Chrysoperla) and the larvae of fireflies (Lampyridae).

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