Extension Communications
3614 Administrative Services Building
Ames, Iowa 50011-3614
(515) 294-9915
2/12/01
- Contacts:
Donald Lewis, Extension Entomology, (515) 294-1101, drlewis@iastate.edu - Elaine Edwards, Continuing Education and Communication Services, (515) 294-5168, eedwards@iastate.edu
Yard and Garden Column for the Week Beginning Feb. 16
Don't Look Under the Mulch
- By Donald Lewis
- Extension entomologist
- Iowa State University Extension
Much has been written about mulch. You probably already know about the good things that happen when you spread wood chips, grass clippings, shredded leaves, bark chips or straw on the soil surface around trees, shrubs, flowers and vegetables. Mulch improves the landscape's appearance. It helps your garden and landscape plants because it conserves soil moisture and lessens temperature extremes. This stuff is so good it can even decrease your workload by preventing weeds.
That's the good news. The bad news is, don't look under the mulch if you are squeamish about bugs and other crawly things. Mulch creates a stable habitat that mimics the natural environment of the forest floor. That's good for plants. It's great for bugs.
Mulches provide shelter, moisture or food for many different insects and their relatives. Most are beneficial. A few are potentially harmful, but their presence is generally not a cause for alarm or treatment.
Predators and Recyclers
Mulch provides a stable habitat where beneficial predators can find a steady source of food. Common predators that live and feed in mulch include rove beetles, ground beetles, lightningbug larvae and centipedes. Centipedes have flattened, elongate, segmented bodies with one pair of legs per segment. They feed on small insects, insect larvae and on spiders. They may look creepy but they are harmless.
Other beneficial organisms are "recyclers" that feed on fungi and decaying plant debris. Their feeding or tunneling breaks down organic material and returns nutrients and humus to the soil. The decomposition of organic mulch by recyclers such as decay fungi, ants, sowbugs, millipedes, springtails and mites converts the mulch into valuable organic matter that improves the soil. Their action also is why mulch needs to be replenished every two to three years.
Some recyclers become a pest when they migrate into buildings as accidental invaders. Millipedes (hard-shelled "worms" that coil into a spiral when dead when handled) and sowbugs are often found in the garage or basement. They hide under the mulch during the day and occasionally crawl indoors by mistake at night. They do not feed upon building structures or furnishings and they can not bite or sting.
A few plant pests hide under mulch. The mulch layer does not attract or cause pest presence but it may increase their abundance by providing ideal living conditions. Examples include cutworms, slugs, snails and earwigs. Treatments are available for combating these plant feeders, so eliminating mulch is not necessary. You may find it advantageous to pull mulch away from the base of the plants.
Ants and Termites
Ants that live in the moist, loose soil under mulch are not harmful to plants, people or structures. They are generally beneficial to the soil and vegetation. Unfortunately, some species wander indoors while foraging for food. Insecticide sprays are only moderately successful at controlling ants that live under mulch.
Carpenter ants nest in galleries chewed into decayed wood such as stumps, logs, firewood, hollow trees and dead limbs. These familiar, large, black ants do not live in or under wood chip mulch. They may forage for food, primarily dead insects, in mulch but they do not live there. Treatments for carpenter ants are best placed in or near the nest sites.
Termites are moderately common but spotty in Iowa. Termites live underground in large, social colonies. Worker termites come to the soil surface (or higher) and feed on wood and other cellulose materials and carry it back to share with other colony members. Termites are recylcers that play an important role in the natural breakdown of wood. Their presence inside a home or other structure, however, can lead to aesthetic or structural damage.
Termites routinely feed on wood chip mulch and other wood products on or in the soil (lumber scraps, boards, firewood, pallets, etc.). However, wood chip mulches do not attract termites that were not already present in the area. Similarly, it is highly unlikely that termites would be introduced into a previously uninfested area by the transport of wood chips.
Termites constantly explore for food by excavating a network of random, pencil-sized tunnels that may extend up to 300 feet through the soil. Presence of moisture favors termite exploration, tunneling and feeding. Any landscape mulch may improve conditions for termite colonies, whether the termites consume the mulch or not. This does not mean you should avoid use of mulch, nor does it endorse one type of mulch as preferable over another.
Keep mulch several inches away from the house foundation. Never allow mulch to cover windowsills or to contact siding as this may provide termites direct and undetectable access into your home. Watch wood chip mulch for signs of termite activity. If you suspect termite activity contact several professional termite control services for inspections and estimates.
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