The Pre-Summer Mosquito and Fly Checklist

Step 1: Eliminate Every Source of Standing Water

Walk the entire property with a 5-gallon bucket and dump every container holding water. Plant saucers, kid pools, tarps with sagging pockets, wheelbarrows, buckets, watering cans, toys, recycling bins, and forgotten flower pots are all prime mosquito nurseries. A bottle cap of water is enough to support a mosquito brood. Tip out anything that holds water, drill drainage holes in containers you want to keep, and store everything else upside down or under cover.

Step 2: Clear Gutters and Downspouts

Clogged gutters hold standing water for weeks and are one of the most common breeding sites homeowners miss because they can't see it from the ground. Clean every gutter run before the spring rains end, flush downspouts to confirm they drain fully, and grade the soil where downspouts discharge so puddles don't pool against the foundation. While you're up there, check that gutter end caps are sealed and that any leaf guards aren't trapping debris.

Step 3: Treat Ornamental Water Features and Ponds With Bti

Birdbaths, rain barrels, koi ponds, and decorative fountains you can't simply drain are perfect candidates for Bti. Bacillus thuringiensis israelensis is a naturally occurring soil bacterium that kills mosquito and fungus gnat larvae but is harmless to fish, pets, birds, bees, and humans. Drop 1 mosquito dunk per 100 square feet of water surface, replace every 30 days, and refresh birdbaths twice weekly. For rain barrels, add a tight-fitting screen lid so adult mosquitoes can't enter to lay eggs in the first place.

Step 4: Pre-Season Drain Fly Cleaning

Drain flies (those tiny fuzzy moths in the bathroom) breed in the biofilm that builds up inside infrequently used drains over winter. The fix is mechanical, not chemical. Pour boiling water down each drain to soften the gunk, then scrub the inside walls with a long-handled drain brush, and finish with an enzyme drain cleaner that digests the remaining biofilm overnight. Hit the basement floor drain, laundry drain, guest bath, and any drain you don't run weekly. Doing this in April prevents the July swarm that shows up when warm weather speeds biofilm growth.

Step 5: Lock Down the Garbage and Compost Area

House flies cycle a generation in 7 to 10 days when temperatures are warm, and the garbage area is their headquarters. Pre-summer, swap any cracked or lidless cans for ones with tight-fitting lids, hose out the inside of every bin (residue at the bottom is the actual attractant), and move bins at least 20 feet from the door if possible. Compost piles need a layer of brown material (leaves, straw, shredded cardboard) on top of every layer of food scraps to suppress flies and odor. Bag meat scraps and fish separately and freeze until trash day.

Step 6: Inspect and Repair Window and Door Screens

Walk the perimeter of the house and check every screen for tears, gaps at the frame, or loose corners. A 1/4-inch hole is enough for a mosquito to walk through. Patch small tears with screen repair tape, replace badly damaged screens entirely, and add door sweeps to any exterior door that doesn't seal at the bottom. If you don't have screen doors on your most-used exterior doors yet, this is the year to add them. They're the biggest comfort upgrade for summer entertaining.

Step 7: Check Soffits, Vents, and Foundation Entry Points

Adult flies and mosquitoes find their way into attics and wall voids through unscreened soffit vents, ridge vents, gable vents, and dryer vents. Replace any missing or damaged vent screens with 1/8-inch hardware cloth. Walk the foundation looking for gaps around pipe penetrations, AC line sets, and the gas meter, and seal them with copper mesh and silicone caulk. Pay special attention to the gap where the siding meets the foundation. It's the most common entry point and the easiest to overlook.