Millipedes, Centipedes And Isopods

Any building can be subject to pest infestations, and most pests invade buildings from their outside harborages. Only a few pests, such as German cockroaches, pharaoh ants, and stored product pests, actually infest buildings by being carried in by the building's occupants. Few outside invading pests are considered serious pests of structures, except for certain species of peridomestic cockroaches and several species of ants.

Many of the pests that enter from outside structures are known as "occasional invaders." Most occasional invader pests are insects; however, arthropods such as millipedes, centipedes, sowbugs and pillbugs (the last two are known collectively as isopods) regularly wander into structures. This article will examine the identification, the biology, and the control of these four types of arthropods.

IDENTIFICATION. Millipedes and centipedes closely resemble each other, both being multi-segmented and possessing numerous pairs of legs. Some millipedes are rounded in body shape while others are flattened; the same holds true for centipedes. The difference between the two is easy enough millipedes have two pairs of legs per body segment, while centipedes have only one pair per body segment. Centipedes are also equipped with a pair of chelicerae (jaws) tipped with sharp fangs, and larger species can inflict a nasty bite.

In general, centipedes crawl faster than millipedes and have quicker movements. They also quickly seek cover when disturbed, while millipedes often curl up or stay still. Some species of centipedes and millipedes can grow quite large, up to 4 or 5 inches or longer, although structure-infesting species are generally less than 2 inches. One species of centipede in Texas that occasionally invades homes grows up to 6 or 7 inches, and is blue-black in color with a reddish head and legs.

Isopods are actually crustaceans, and are related to shrimps, crabs, and lobsters. Sowbugs and pillbugs are grayish, oval in shape, and grow up to ½ inch in length. Both have seven pairs of legs as adults. Sowbugs are more flattened than pillbugs, and are identified by the two long appendages that extend from their rear. Pillbugs lack these appendages, and are easily identified by their ability to roll up into a ball. For this reason, they are often called "roly-polies."

BIOLOGY. In general, millipedes, centipedes, and isopods prefer to live in moist conditions where sufficient decaying organic matter is present. These arthropods soon die when they wander into areas that have little moisture, such as the inside of a building. Outside, they will be found under heavy leaf litter, ground covers such as ivy, landscape timbers, mulch, and piles of firewood or debris.

• Millipedes. Female millipedes lay up to 300 eggs during their lifetime, usually in moist soil. The eggs hatch into tiny "larvae" that have three pairs of legs and seven body segments. As the larvae grow and molt, they continue to add body segments, each equipped with two pairs of legs. Their life cycle from egg to adult usually takes two years, although some species require up to five years.

Millipedes use a variety of methods to protect themselves from predators. While they molt, millipedes occupy molting chambers that they dig into the soil. When disturbed, some millipedes curl up into a ball, while other species are capable of expelling a noxious chemical that is irritating to predators. These secretions contain hydrocyanic acid, iodine and quinone, and the secretions of some millipedes can cause irritation in human skin.

Millipedes feed on organic debris found in their living environment, which is why they are common in leaf litter, lawns, and landscape mulch. When conditions are excellent for survival several years in a row, millipede populations can explode, leading to a phenomenon known as "millipede migrations."

Larger millipede populations are most common in heavy leaf litter, although they can occur in well-watered lawns. If the environmental conditions within the millipede habitat turn unfavorable, the millipedes begin to venture out in search of better conditions. Conditions such as drying out or too much moisture within the habitat are the most common triggers for a millipede exodus. These en masse migrations can be quite disconcerting to homeowners or businesses that happen to be in the path of the migration. A "sea" of millipedes crawl over, across, through, or up any obstacle in their path, and can be unstoppable. They enter buildings through any crack or hole, and even enter under doors. Large piles of millipedes can accumulate every day on patios, in garages, in basements, and even inside homes and businesses.

Some reports detailing millipede migrations border on the amazing. One farmer mentioned in the Mallis Handbook of Pest Control reported removing a half bushel of millipedes every morning from his back porch. On at least two reported occasions in Europe, millipede migrations crossing railroad tracks caused train travel to be suspended because crushed millipede bodies made the tracks too slick for safe travel.

The buildings that most commonly experience millipede migrations are those located in wooded areas where leaf litter accumulates under trees. Leaves provide the best of everything a millipede needs to survive. Although less common, millipede migrations have been known to occur out of lawns that are heavily shaded and well-watered. Migrations originating from lawns typically are less severe than those occurring from leaf litter.

• Centipedes. Most centipedes live outdoors under rocks, logs, leaf litter, and mulch. One species, the house centipede (Scutigera coleoptrata), lives inside structures, and is recognized by its extremely long legs. These long legs and the house centipede's quick movements can make it appear larger than its actual 1½- to 2-inch length. This centipede also has three dark stripes down the length of its body, and the legs are banded with white stripes.

Centipedes are predators, and feed on insects and worms. The house centipede will capture and feed on spiders. Most centipedes remain outdoors and rarely enter structures, and if they do, they typically die a quick death. The house centipede, however, breeds inside structures, and is rarely found living outside. It prefers moist basements and crawl spaces in which to live and breed, but an occasional centipede may be seen scurrying up a wall in the living area of a home. Most infestations of this centipede are small, but under the right conditions, such as an overly moist crawl space, larger populations can occur.

• Pillbugs and Sowbugs. As stated earlier, pillbugs and sowbugs are isopods, and are the only true terrestrial crustaceans. Like their water-bound crustacean relatives, pillbugs and sowbugs do require high-moisture conditions to survive. In fact, they lack the ability of insects and other arthropods to prevent or limit body water loss, and easily succumb to dry conditions. For this reason, sowbug and pillbug invasions inside structures are limited, and are usually associated with excessive populations next to buildings.

Isopods are commonly found living together with millipedes and centipedes in mulch, in leaf litter, and under items. Pillbugs and sowbugs feed primarily on decaying organic matter. They have also been found to feed on and damage the new roots and leaves of plants, particularly bedding plants. These arthropods are also commonly found harboring in moisture-damaged wood, where they feed on the decaying wood fiber from which they will produce a fine, granular frass. Sowbugs and pillbugs are incapable of causing damage to solid wood, and are only a secondary invader to wood that is already seriously damaged.

CONTROL. Most situations involving these arthropods are fairly easy to correct. The exception is millipede migrations, which will be covered in detail later. By following the steps outlined below, pest management professionals can achieve successful control in most situations.

• Harborage Removal. Removal of the leaf litter, mulch, or other harborages used by these arthropods is critical to long-term success. In fact, many cases involving centipedes, isopods, and even millipedes can be effectively controlled by performing this one task.

Leaf litter and mulch are the two most crucial harborages, especially for millipedes and isopods. Removing the items that hold the moisture creates conditions unsuitable for their survival. This act alone keeps populations to a minimum, making it less likely that the pests might enter a building. Harborage removal must be enacted from the foundation to as far away from the building as possible, although the foundation area is most important.

Landscape mulch will be the most difficult harborage to eliminate because customers need to maintain mulch around landscape plantings. As a rule, however, mulch should be kept to a thickness of no more than 2 inches, and should not be placed within 6 to 8 inches of the foundation. Thicker layers of mulch hold more moisture, creating conditions suitable for large populations of pillbugs, sowbugs, and millipedes.

Installing a vegetation- and mulch-free barrier up to 18 inches wide along a building's foundation is very helpful in limiting problems with these and other pests. This step is most easily achieved for commercial buildings, and is required by many food facilities and factories. For best results, the barrier should consist of a few inches of gravel spread over a sheet of plastic.

• Exclusion. Sealing cracks and holes in a building exterior helps limit potential entry points for any pest, and should be a step included in all pest management programs. Weep holes in brick veneer buildings are common entry points that cannot be sealed. Small screens designed for use in weep holes may be available commercially.

• Moisture Control. Since moisture is a critical component for the survival of millipedes, centipedes, and isopods, it makes sense to correct any condition that creates excessive moisture in areas where these pests could thrive.

Improperly installed or placed sprinkler systems are notorious for creating excessive moisture along foundations. Sprinklers should be positioned so they do not spray onto or within 2 feet of foundations. Landscape beds are best watered using soaker hoses that distribute water near the plants. Customers should be advised to adjust their sprinkler systems when they are contributing to a pest problem.

Rain gutter downspouts should be directed away from the building's foundation. In many cases, the downspout is positioned so that it directs water at the foundation. It is best if the downspout is equipped with a tray or a hose to spread the water several feet from the foundation.

In cases where house centipedes, millipedes, or isopods are thriving in a moist crawl space, improving the foundation ventilation and installing a moisture barrier is necessary. In overly wet conditions, a sump pump or other more extreme method may be necessary to relieve excessive water in a crawl space.

• Insecticide Applications. In most cases involving millipedes, centipedes, pillbugs and sowbugs, the application of insecticides is limited to a few spot applications. As a general rule, a service technician should carry a compressed air sprayer containing a suitably labeled insecticide as he or she inspects around a building's exterior. As items are lifted or mulch is pulled back to inspect, exposed pests can be treated directly. Following this procedure saves time, and is the most judicious use of an insecticide.

In cases where sowbugs, pillbugs, or millipedes are regularly being seen inside a building, it generally means a significant population is present next to or near the building. Once the source(s) of the population is (are) found, the appropriate insecticide can be applied to the site of the source(s).

If large numbers of pests are living in mulch or heavy leaf litter, a general treatment of the entire area may be necessary. When heavy leaf litter is involved, the leaves should be removed prior to any application. If mulch is involved, the mulch will need to be raked back to expose the pests, treated, and then raked back into place. An additional application to the top of the mulch may be helpful. A wettable powder or microencapsulated insecticide works best in these situations.

MILLIPEDE MIGRATIONS. By far, the most difficult situation involving these occasional invader pests is a millipede migration. Fortunately, migrations are not common. But when they do occur, a pest management professional can expect to spend many hours attempting to provide his customer with some relief. In many cases, total relief will not be achievable, and at the very least, it usually takes two to three weeks of constant attention before the last millipede is seen. It may well be that the "success" in control is due more to the migration"petering out" than to the efforts of the customer and pest management professional.

The first step in dealing with a millipede migration is to find the source of the infestation. Are they coming from leaf lit ter in a wooded area, an adjacent field, or even the lawn? It should be easy to determine a source, because innumerable millipedes will be present. If possible, observe the direction from which the millipedes are crawling. This should point out the direction of the source.

Hopefully, the source of the millipedes will be on the customer's property and not a neighboring property. If not, quick relief or even any relief may not be possible. Removal of the harboring material in which millipedes are living is a crucial step to stopping or lessening the migration. If the source is on an adjacent property, the customer will need to seek permission to do something on that property to stop the migration.

When possible, pick up and bag the leaf litter the millipedes are using as harborage, even if the leaves are on the ground of a neighboring wooded area. In doing so, much of the millipede population can be removed with the leaves. Piles of debris should be removed and disposed of, and firewood should be stacked at the far end of the property.

An appropriately labeled wettable powder or microencapsulated insecticide can be applied to areas where millipedes are found, as well as in a band up to 10 feet from the foundation.

Insecticide dust should be injected into exterior cracks and holes, and holes should be sealed. Using an Actisol or similar machine, insecticide can be injected behind brick veneer through the weep holes. Follow this with an application of a residual dust insecticide, and then install weep hole screens if they are available. Treatment inside cracks prior to sealing is important, because millipedes are likely to have already crawled into the cracks and into the voids behind them.

In cases where a lawn is involved, have the homeowner mow the lawn as low as possible for the type of grass involved, and instruct him or her to cut back the lawn watering schedule. An application with an appropriately labeled wettable powder insecticide can be effective. Another option is Ficam granules, which have also worked very well for the author. Follow-up visits every day or every other day are necessary to reinspect and possibly to make additional applications, should the need arise. Total success in preventing all millipedes from entering a structure are rare. The customer should understand this and be prepared to deal with millipedes, dead and alive, on patios, decks and driveways, and even in pools. It may be possible to keep millipedes out of a house, but to totally stop them from being seen outside may be asking too much. Persistence and customer patience are crucial in dealing with millipede migrations.

HOUSE CENTIPEDES. When house centipedes are seen inside structures, usually only one to several are involved. In such cases, limited insecticide applications to cracks and voids in the area where the centipede was sighted will provide results. In a situation where numerous house centipedes are present, more extensive inspection and treatment is generally warranted.

Crack and crevice and spot treatments will be necessary in areas where house centipedes are seen. However, the most effective applications will be in the moist areas where the source of the centipedes is likely to be located. If a moist basement or crawl space in involved, the customer should be advised to take steps to improve the conditions. This step alone will help long-term. In addition to crawl spaces and basements, inspect and treat voids under bathtubs, and check for poor ventilation in attics.

Stoy A. Hedges is manager of technical services with Terminix International, Memphis, Tenn.