Many permaculturists and others with a special interest in sustainability are aware of the concept of indicator species. An indicator species is one that signals the overall health of an ecosystem.
A knowledge of indicator species can be useful in the garden. The preponderance of a particular weed, for instance, can tell us about soil conditions such as pH, texture, and nutrient balance.
But while weeds and other plants are regularly used as indicator species, many gardeners forget to regard insects in this light. To many of us, insect pests are not a meaningful signal—just a problem.
By paying closer attention to what nature is telling us, however, we have an opportunity to get to the root of the matter and bring our gardens back into balance.
Insects and What They Indicate
An abundance of the following common garden insects and related creepy-crawlies (both good and bad) indicates the following:
- Ants. Presence of aphids, scales, or whiteflies.
- Aphids. Excess nitrogen; insufficient magnesium, sulfur, molybdenum, and/or boron.
- Blister beetles. Insufficient moisture; presence of grasshoppers.
- Boxelder bugs. Presence of boxelder trees, or perhaps other maples.
- Cabbage loopers. Excess nitrogen; insufficient magnesium, sulfur, molybdenum, and/or boron.
- Centipedes. Moisture; iron deficiency.
- Corn borers. Excess nitrogen; insufficient magnesium, sulfur, molybdenum, and/or boron.
- Corn earworms. Excess nitrogen; insufficient magnesium, sulfur, molybdenum, and/or boron.
- Flies. Decaying organic matter.
- Grasshoppers. Insufficient moisture.
- Ladybugs. Warmth, light colors, and/or aphids.
- Leafhoppers. Low-sugar plant tissues.
- Monarchs. Presence of milkweed.
- Mosquitoes. Standing water or poorly drained turf.
- Pillbugs. Moisture, shelter, and decaying organic matter.
- Slugs. Moisture.
- Snails. Moisture.
- Spiders. Insect infestation.
- Squash bugs. Shelter (including mulch).
- Stinkbugs. Weed overgrowth; absence of predators (may be caused by pesticide use).
- Tomato hornworms. Excess nitrogen; insufficient magnesium, sulfur, molybdenum, and/or boron.
A Few Tips on Using Indicator Species
Keep in mind that seeing one or two of anything is not a reliable indicator. A swarm is a much more useful signal.
Also note that there is much we do not know about insects as indicator species. You may look at the above list and be baffled as to why you have an infestation at all. Nevertheless, an overabundance of one type of insect definitely signals some type of imbalance, even if the cause is not readily obvious.
Nearly all insect pests can be controlled by keeping plants healthy in general. That means providing enough water, keeping weeds in check, and paying attention to soil health.