How to Remove Fish Flies and Spider Webs from Your Siding

If You Live Near the Water, You Already Know

Every June and early July, homes along Lake St. Clair get a visitor that residents further inland cannot picture. Fish flies, which are mayflies, emerge from the lake bottom in numbers dense enough to show up on weather radar, and they coat everything.

Harrison Township, St. Clair Shores, New Baltimore, Grosse Pointe and the Selfridge corridor take the worst of it. Homeowners in Macomb Township or Washington Township twenty minutes inland may never see one.

The nuisance is obvious. What many homeowners do not expect is how much harder the residue is to remove once it has sat through a few hot weeks.

Why Fish Fly Residue Stains Siding

The insects themselves do not damage property; the National Pest Management Association classes mayflies as a nuisance pest. The problem is what is left behind. Adults live only a day or two, so they die against walls, screens and lights in enormous numbers, and their soft bodies break down into a sticky organic film.

Three things then happen fast:

• The film bonds to the surface. Left on a sunny wall through a stretch of July heat, it dries hard and can leave a shadow that stays after the bodies are gone.
• It bakes on. Siding in direct sun gets far hotter than the air. What was soft residue in the morning can be stuck fast by evening, and it gets harder to remove every day.
• It feeds mildew. Decomposing organic matter in gutters, window channels and behind shutters becomes a nutrient source for the mildew and algae you pay to remove.

What Not to Do

Two quick fixes make the residue worse.

Do not scrape or scrub dry. Fish fly bodies are gritty. Dragging them across dry vinyl with a brush or a putty knife grinds that grit into the surface and leaves fine scratches that hold dirt.

Do not blast them with high pressure. A hard stream smears residue into the surface texture rather than lifting it, and a stream aimed upward forces water behind the panels, a bad combination on a wall already carrying decomposing organic matter. High pressure can also crack aged vinyl at panel edges.

The Correct Removal Method

1. Rinse first, low pressure. A generous low-pressure rinse floats off the bulk of the bodies without abrasion. Work top to bottom.
2. Apply a cleaning solution and let it dwell. The solution breaks down the remaining bonded residue chemically. Give it several minutes; this is where the cleaning happens. For a do-it-yourself wash on vinyl, a mild soap and water with a soft brush follows the Vinyl Siding Institute's care guidance.
3. Soft-brush the heavy areas only. Under eaves, around porch lights, in window channels: a soft brush on an already-wet, already-treated surface, never dry.
4. Rinse thoroughly again, including window frames, sills, screens and the gutter face where bodies accumulate.
5. Check the gutters. After a heavy hatch, gutters along the lakeshore can fill with a decomposing mat that blocks flow and smells. It needs pulling out, not just rinsing along. A gutter that holds standing water also becomes a mosquito problem; see clogged gutters and West Nile mosquitoes.

This is the process we run on lakeshore properties every summer, and it is a common reason Harrison Township homeowners book a professional house washing in late June or July.

Spider Webs: The Spring-to-Fall Version of the Same Problem

Waterfront homes tend to carry larger spider populations than inland homes, for a simple reason: the spiders are there for the insects, and near the lake there are more insects. Through the warm months, webs accumulate fastest under eaves, in soffit corners, around exterior lighting, behind shutters and along railings.

Two things make webs worse than they look:

• Webs are sticky and hold dirt. An abandoned web becomes a gray mat of trapped dust and debris that stains the surface underneath.
• Spider droppings stain. The small dark specks on siding under eaves are droppings, and left long enough on vinyl or painted surfaces they can leave marks that outlast the web.

A knocked-down web is often rebuilt within days. A professional wash keeps webs away longer because it removes the residue and insect debris that made the spot attractive, not just the web. Other insects stain siding the same way; fall brings boxelder bugs and lady beetles to the sunny walls.

When to Schedule Around the Hatch

Lakeshore homeowners often pair the post-hatch wash with gutter cleaning, since both problems arrive on the same schedule.

The Bottom Line

Fish flies are a fact of life within a couple of miles of Lake St. Clair, and you cannot stop the hatch. You can reduce how many land on the house: mayflies are drawn to light, so the National Pest Management Association suggests yellow bulbs in place of white ones, and keeping porch and landscape lights off on hatch nights helps. What you can control most is how long the residue stays on your house. A wash within two weeks after the hatch ends is routine maintenance. The same wash in September is a stain-removal project with no promise it fully comes out.