Moisture Pests

Moisture pests can also be thought of as "Pests That Wouldn't Be There Unless There Were Structural Issues in Your House That Could Cost You a Lot of Money to Fix So You Should Thank Them if They Help You Identify Issues Early".

What Do Moisture Pests Look Like?

Moisture pests represent a diverse collection of organisms we usually ignore outdoors but don't want found indoors. This includes,, ,, isopods (pillbugs and sowbugs; many legs, gray in color), and mold.

Should I Worry About Moisture Pests?

For the most part, moisture pests are considered a nuisance. However, two pests that exploit moisture in wood can cause additional structural problems: carpenter ants and termites. These insects are covered in their own sections (see Ants and Termites). Additionally, mold can be human health issue.

It is important to mention here that the underlying reason for these pests in an area is a moisture problem.

Why Do I Have Moisture Pests?

As the name implies, these organisms are pests because of moist conditions in or immediately adjacent to the home. For example, unfinished basement/crawl space with dirt floors, basements with high humidity, water leaks under tubs or in walls, mulch against the foundation, or improper drainage of water away from the home (including filled, damaged or improperly installed gutters, and windows sills that are not pitched correctly) are all sources of moisture.

Keep in mind that the moisture is the problem, and the pests are the symptom. Effectively managing moisture pests requires that the moisture issue be addressed first.

How Do I Manage Moisture Pests?

The most important consideration for eliminating moisture pests is to identify and remediate the moisture source. The US Environmental Protection Agency (EPA) recommends that indoor moisture levels do not exceed 60%, and ideally fall between 30 and 50%. While most of us can notice humidity or the dampness in any room, you can test the moisture present by using an indoor humidity gauge available from most hardware stores. The list below includes site-specific tips to reduce moisture:

In the basement and crawl space - these steps can address: camel cricket, spiders, house centipedes, millipedes, isopods, mold.

  • Install ventilation in dirt-floor basements and crawl spaces. Vents can be active (a fan moves air) or passive (air flows naturally), and should be rodent proof. Consider using hardware cloth with quarter (1/4) inch openings. Note that the small opening size of window screening can limit air flow and will not prevent rodent entry.
  • Use a vapor barrier to reduce moisture associated with dirt-floor basements and crawl spaces. Thick plastic is used to cover the soil, is affixed to vertical surfaces like foundation walls and support piers, and seams are sealed with specialized tape. DIY and for hire options are available.
  • Use a dehumidifier to reduce indoor humidity to less than 60%.
  • Use moisture-locking paint products to block the porous nature of foundation materials (concrete hollow block; poured cement).
  • Insulate basements to buffer against temperature fluctuations and reduce the formation of condensation.

Fix water leaks

Springtails (small insects that jump when disturbed or poked) can indicate a moisture problem. Leaks may be out of sight, and the accumulation of moisture in flooring or other areas can provide the habitat necessary for springtail survival. Search for hidden leaks when springtails, booklice, silverfish, carpenter ants, or other problems arise.

  • Check for poor pipe connections, cracked pipes, or improper seals for pipes located in kitchens, bathrooms, basements, utility rooms and walls.
  • Check for sweating pipes, which are typically cold-water pipes in a heated/warm area, or hot water pipes in a cold area. Condensate can drip from pipes and create a moisture problem. Pipe-insulating materials are available to reduce problems associated with condensation, but may also become saturated with condensate in certain conditions.
  • Ensure that drip pans are not overflowing. This is particularly important for refrigerators, where leaky drop pans may not be detected behind a refrigerator.


  • Ventilation is a must in attic spaces. Moisture problems can occur if there is not proper airflow accomplished by the presence of two or more windows (on opposite sides to create a draft), soffits and/or ridge vents. An especially worrisome problem occurs when bathroom or clothes dryer vents are directed into the attic rather than outside the home. In addition to pest issues, this can lead to mold problems and ultimately reduce the structural integrity of the support beams.


These steps can address: camel cricket, springtails, ground beetles, spiders, house centipedes, millipedes, isopods, carpenter ants.

  • Create three-to-six-foot gap between plants and the home. Plants, especially low-growing species used in landscapes, are a source of moisture. When in close contact with a building, they create an environment that is conducive for many types of pests.
  • Avoid having mulch in direct contact with the home. Use of mulch in landscapes adds moisture, as a primary use of this substrate is to maintain soil moisture for plant health. There are countless organisms that live in the moist, mulch environment, including millipedes, isopods, springtails and other decomposers. Spiders and house centipedes visit these moist environments to hunt for, and feed upon other arthropods. Therefore, removing mulch borders around the home eliminates the decomposers and predators found in these habitats. Mulch borders can be replaced with Vegetation Free Zones. These are 18 to 36-inch barriers made of crushed stone that do not include any plantings.
  • Ensure proper drainage away from the home. Several situations contribute to moisture issues at the foundation level. This includes rainwater moving downhill towards the house/foundation, gutters not functioning properly (clogged; too small for water volume), or downspouts that fail to move water away from the home. Inspect the home during a rain event to see if water is leaking from gutters, and look for evidence of standing water after a rainfall. Windowsills that are not pitched correctly or instances where window weep holes are filled, can lead to moisture problems in the window frame.