Excess moisture increases pest pressure

Warm weather not the only cause of high humidity levels in condos
Wednesday, March 7, 2018
By Dr. Alice Sinia

High humidity levels may be associated with the summertime, but moisture issues can be problematic well into the fall and winter because of humidity-generating activities and circumstances such as cooking, hot water usage, water leaks, air leaks and even the building’s exterior. If a condominium property has moisture problems, its board and manager are sure to have unhappy residents on their hands.

In addition to making living spaces uncomfortable, indoor moisture problems can lead to structural damage, health and pest problems. If the root cause of moisture isn’t resolved quickly, it can cause significant damage and impact a condo corporation’s bottom line.

Excess moisture in condos can harm residents and staff alike. It can cause bacteria, mould and mildew growth, which poses health threats for sensitive individuals and can cause allergies and asthma. Mould and mildew in the walls can be difficult to detect without professional diagnosis, but is associated with visible signs of water damage such as peeling paint, warped wood, wall bubbling, discolouration and corrosion of metal. While some of these consequences are purely aesthetic, others can damage the structural integrity of a property.

Even if residents don’t immediately notice these signs, they will surely notice increased pest activity that can develop as a result. Pests are attracted to condos for the food, water and shelter they provide. If a property has excess moisture, it becomes even more attractive to the pests seeking out water sources, as well as pests that feed on mould and mildew.

Moisture attracts certain types of insects


These tiny, jumping insects are attracted to areas of high moisture because they rapidly lose water from their bodies. They flock to kitchens, bathrooms and laundry rooms where moisture is common, invading through gaps and openings around utility pipes, cracks and crevices in wall foundations and window screens and sills. The insects feed on decaying vegetation, bacteria and fungi.

Plaster beetles

These critters feed exclusively on spores and vegetative parts of mould, mildew and other fungi. Most species live outdoors, but there are a few that invade and infest structures especially in areas that are conducive to fungal growth, such as damp basements and crawlspaces, inside walls and on damp fiber and carpet.

Fungus beetles

These critters are attracted to musty odours and are small enough to get through vents or screens. Like plaster beetles, they feed exclusively on fungi and are found indoors in areas with moisture problems.

Foreign grain beetles

These scavengers feed on fungus, mouldy grain and dead insects. Infestations often start inside wall voids and become noticeable when beetles emerge from the baseboards.

Psocids (Booklice)

Despite their resemblance, these critters are not true lice. They are typically found in areas with high humidity because they can easily lose water from their bodies. Mould is their primary diet and psocids have been known to infest bath traps and air conditioning drain lines.

Common pests such as cockroaches, ants and rodents also can be found more often in buildings with excess moisture.

Managing these types of pests is a team effort, and a successful Integrated Pest Management (IPM) program will require cooperation from both residents and property management. There are a few things that can help reduce these moisture-related pest pressures:

Managing moisture-related pest pressure

Property managers can take the following steps to address both excess moisture and the pests that it attracts:

  • Vent clothes dryers and unit heaters to the outdoors as much as possible. These appliances produce water vapour and can increase humidity.
  • Inspect vent ducts regularly and clean them at least once per year.
  • Inspect, clean and repair drains and roof gutters regularly.
  • Respond promptly to water leaks. If damp or wet surfaces are resolved within 24 to 48 hours, mould and mildew should not grow.
  • Be sure that the ground slopes away from the foundation of the building. This helps prevent water from pooling around the foundation.
  • Seal cracks, crevices and gaps around utility lines, window sills and doors.
  • Eliminate indoor condensation with:
    • Increased ventilation indoors
    • Air conditioning systems with dehumidification
    • Exhaust systems in bathrooms and kitchens
    • Airtight HVAC systems

Property managers can also share the following tips with residents:

  • Keep air conditioning units on during warmer days to lower humidity levels.
  • Turn on exhaust fans when showering and cooking to remove moisture from the air.
  • Leave the washing machine doors open when not in use to allow water to dry.
  • Report moisture collecting on windows, walls or pipes immediately and dry the affected areas.
  • Report plumbing problems and leaks promptly and ensure they are repaired.

To prevent pest problems related to excess moisture, it is critical that all residents take steps to reduce humidity in their units. To get residents on board, review the importance of moisture control at the next corporation meeting and send out an email or newsletter to help educate individual unit owners.

Given its potential to cause pest infestations, property damage and health risks, excess moisture is not a problem that a condo board or manager wants to have. Pests such as springtails and plaster beetles are often a sign of an underlying moisture, mould and mildew issues, which should prompt a call to the corporation’s pest management provider and steps to reduce humidity levels.

Alice Sinia, Ph.D. is quality assurance manager – regulatory/lab services for Orkin Canada, focusing on government regulations pertaining to the pest control industry. With more than 15 years of experience, she performs analytical entomology as well as provides technical support in pest/insect identification to branch offices and clients. Alice can be reached at [email protected]

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