Mosquitoes
Mosquitoes lay eggs in standing water, and some species need only a small amount for a week or so to develop. Clogged gutters hold water in low spots behind leaf debris, and gutters that sag or are pitched wrong hold water even when clean. Local health departments routinely list clogged gutters among the places to check; the DuPage County Health Department’s “mosquito control begins at home” guidance, for example, includes keeping gutters clean along with emptying containers and bird baths.
- Keep gutters clear, especially in late spring and summer.
- Look for standing water a day after rain; if water stays, the gutter needs re-pitching or a sag fixed.
- Screen rain barrels with fine mesh and keep lids tight. See rainwater harvesting.
- Make sure downspout extensions and buried lines do not hold water.
Termites
Subterranean termites live in the soil and need moisture. Extension services, including the University of Kentucky’s entomology program, list gutters and downspouts among the first things to check: properly working gutters, downspouts and splash blocks that carry water away from the foundation reduce the damp soil termites favor. Overflowing gutters also soak fascia, soffits and siding, and wet wood is easier for termites and wood-decay fungi to attack.
- Carry roof water several feet from the foundation onto ground that slopes away.
- Fix leaks and overflow that keep walls and trim wet.
- Keep mulch thin next to the foundation and away from siding.
- Replace rotted fascia before installing new gutters. See fascia repair before new gutters.
Termite pressure is highest in the South and on the Gulf and Atlantic coasts, including Jacksonville, New Orleans and Houston.
Carpenter ants and wood-boring insects
Carpenter ants do not eat wood, but they excavate nests in wood that is already damp or decaying. Leaking gutters and rotten fascia are classic nesting spots. If you see sawdust-like material (frass) below the eaves or large black ants at the roofline, check for wet wood near the gutters.
Wasps and hornets
Paper wasps and yellowjackets build nests under eaves, behind downspouts, inside gutter ends and in the gaps behind gutters. Nests are most active in late summer. Check before any gutter work; gutter crews run into them often. Removing nests from high places is safer for a professional. Sealed end caps and gutters tight to the fascia leave fewer nesting spots.
Cockroaches and other moisture lovers
American cockroaches, silverfish, earwigs and millipedes all thrive in damp areas around the foundation and in wet leaf debris. Many of them move indoors when conditions outside change. Dry soil and clean gutters make the edge of the house much less inviting.
Birds
Birds nest in gutters, especially at corners and behind downspout outlets, which blocks drainage. Guards keep them out. In many states, active nests of native birds are protected, so wait until the nest is empty before removing it or ask local wildlife authorities for guidance.
Rodents and squirrels
Squirrels and rats use gutters as highways and nesting spots, and gutters and downspouts can give them access to the roof. Gaps between the gutter and fascia or damaged soffits may let them into the attic. Keep overhanging branches trimmed back from the roof, seal soffit gaps, and use guards that fasten firmly. Squirrels sometimes chew on heat cables and plastic guards, so check them each fall.
Moss, mold and mildew
Not pests in the insect sense, but damp gutters and walls grow moss and mildew, especially in shady, humid places. Moss washing off the roof also clogs gutters. See moss and gutters.
Crawl spaces and basements
Water that pools next to the foundation does not stay outside. It soaks into crawl spaces and basement walls, raising humidity under the house. Damp crawl spaces attract termites, carpenter ants, cockroaches, silverfish, spiders and rodents, and they feed mold and wood rot in joists and subfloors. Many crawl space problems start with downspouts that discharge right at the foundation or buried lines that are clogged. Before spending money on crawl space encapsulation or dehumidifiers, make sure roof water is carried well away from the house.
Seasonal checklist
- Spring: clear seeds, blossoms and nests; check for standing water as mosquito season starts.
- Summer: look for wasp nests under eaves and behind downspouts; check extensions after mowing.
- Fall: clear leaves before winter; trim branches that give squirrels access to the roof.
- Winter: watch for ice and for animals seeking shelter in soffits and attics.
The common thread: water in the wrong place
Almost every gutter-related pest problem comes back to water that is not going where it should:
- Standing water in the gutter: mosquitoes
- Water running behind the gutter: wet fascia, rot, carpenter ants and termites
- Water at the foundation: termites, wet basements and crawl spaces
- Debris in the gutter: nesting birds, insects and rodents
Fixing the gutters fixes much of the problem.
What helps most
- Guards that keep debris out, so gutters stay dry between rains. See are gutter guards worth it?
- Correct pitch, so water does not sit. See how to measure for gutters.
- Downspout extensions that carry water well away from the house. See downspouts and your foundation.
- Drip edge or gutter apron, so water does not run behind the gutter. See drip edge and gutter apron.
- Seamless gutters with sealed corners, fewer leaks and fewer hiding spots. See seamless vs. sectional.
- Trimmed trees, fewer leaves and fewer routes for squirrels.
Gutter guards and pests
Guards keep leaves, needles and seeds out, which removes the damp debris mats that hold water for mosquitoes and give insects and birds a home. Fine metal mesh guards keep out most debris and animals; foam and brush inserts can themselves hold moisture and debris if not cleaned. Whatever guard you choose, it should fasten firmly so squirrels and birds cannot lift it. Guards also make it easier to see standing water, because the gutter stays cleaner. They are not maintenance-free: check them twice a year and after storms, and clear anything that builds up on top.
When to call a pest professional
Gutters can remove conditions that attract pests, but they do not remove an active infestation. If you see mud tubes on the foundation, discarded termite wings, sawdust below the eaves or large wasp nests, call a licensed pest control professional. Many states license pest control operators; ask for the license number.