Frequent rains favor several arthropods that do well under humid or wet conditions. These include springtails, pillbugs, gnats, and millipedes.
Springtails (small, wingless insects that hop, Figure 1) are among the most numerous soil arthropods. There are several species ranging in appearance from straw-colored to black. They can be very abundant in humid or moist areas in landscapes or around foundations where they feed on fungi and bacteria growing on decaying plant material. Springtails can enter homes from around foundations, entry doors, or openings to basements or crawlspaces.
Springtails are often temporarily invaders in homes or buildings, but they usually die in a few days because of low moisture in the air indoors. However, they can survive for some time under humid conditions. While harmless, they are a nuisance and a persistent infestation may follow flooding or problems with moisture leaks or condensation.
Infestations located in limited areas can be killed by directly misting with a weak concentration (about 1%) of dishwashing soap in water; this kills the insects by direct contact and does not leave a residue. It should end temporary problems but is not sufficient for persistent infestations.
Prolonged presence of springtails often means excess humidity or moisture. Iincreasing air circulation with fans, or using a dehumidifier or air conditioner may be needed to correct this. In these situations, an insecticide treatment may be needed to knock down springtail numbers quickly. It can be applied to cracks and crevices or as spot treatments to infested areas where springtails occur in the house. Read and follow all label directions to assure that the pest and location of application are on the label. Keep children and pets away from sprayed areas until the insecticide dries. Insecticide treatments are a temporary measure; exclusion and reduction of humidity are keys to ending persistent problems.
General insecticides used in the home for control of cockroaches will kill these insects, but treatments must be placed at their sources, and cleanup should come first. General sprays over floors or other areas will not be effective. Sticky traps can be placed around the home in an attempt to pinpoint the areas that are the sources of these insects.
Outside the home, remove excessive mulch and moist leaves, prune shrubbery and ground covers, and eliminate low, moist areas around the house foundation to permit proper air circulation. Remove wet, moldy wood or other moldy items.
Barrier insecticide treatments are usually applied to the walls and soil immediately surrounding the house. The area treated should be about 3 feet up the wall and 6 feet out from it, depending on the product label. Treatments should concentrate on steps and damp areas. It may also be necessary to treat mulched areas. Applications should be made in the afternoon or early evening because springtails will be most active then. Because of the moist conditions and high organic matter in areas of treatment, it is usually necessary to apply treatments at regular intervals to maintain control.
Pillbugs (including sowbugs, rolypolys, and woodlice) are small armored creatures that live in leaf litter, compost piles (Figure 2), or almost any site that provides protection, humidity, and food in the form of dead wood or vegetation. Pillbugs can move relatively long distances, especially under damp, humid conditions resulting from frequent rains. Those living around foundations can become accidental invaders by entering through gaps around doors, windows, etc. Except for musty basements and crawl spaces, indoor humidity is too low for them to survive for more than about a day. This puts a premium on exclusion as the main means of dealing with them, rather than insecticide applications.
Pillbugs, along with millipedes and earthworms, are important decomposers, so they play a vital role in the food web. Frequent rains favor their development, thus encounters become more likely under those favorable conditions.
If pillbugs reach nuisance levels indoors, consider pruning landscapes to increase penetration of sunlight and improve airflow and drying. Remove wet, moldy wood or decaying organic matter from near foundations.
Non-biting gnats or midges (Figure 3) are common names for several species of small, non-biting flies that can breed in accumulations of standing water, ponds, or lakes—the same types of situations that can produce mosquitoes. They cannot bite or feed, and individuals live for only a few days. However, emergence can occur over a long period of time, causing a chronic problem, especially during wet spells. Large numbers can emerge and become severe nuisances. These gnats are not strong fliers, so their flight range is limited, but they can be aided by winds. Because they are attracted to lights, many can collect on or around houses and buildings.
There are many potential sources of gnats around a landscape or community. The larvae or immature stages of some species develop in wet soils and seepage areas that have large amounts of organic matter; others can develop in ponds or lakes. Fortunately, most sites will dry up and not be suitable for gnats in a few days, but species that develop in permanent bodies of water can be a chronic problem.
The life cycle of these insects (egg, larva, pupa, and adult) can take just a few days or several weeks, depending on the species. There can be several generations during the year. The larvae develop in wet areas or standing water where they feed on suspended organic matter or muck on pond bottoms. Stagnant water makes an ideal breeding site because of the presence of the microorganisms that serve as food.
Difficult to Manage
Gnats are a difficult problem to control with insecticides because of the lack of treatments available for the aquatic sites where they breed. Not only are there potential negative environmental impacts when insecticides are applied to water, but many gnats live in the bottom muck of ponds that are difficult to treat with the few products that are available.
Millipedes (Figure 4) are scavengers that feed on decaying plant matter and occasionally on tender root tissue or plant foliage.
They are abundant under forest floor litter, landscape mulch, and in grass thatch. These sites provide them with food, shelter, and moisture. Millipedes are most active at night and stay out of sight during daylight unless abundant rainfall, drought, seasonal changes, or behavior patterns prompt them to move.
Sweep up and discard accumulations of millipedes present on hard surfaces, if practical. The hard exoskeleton of these arthropods reduces the effectiveness of insecticide applications.
By Lee Townsend, Extension Entomologist