Flies Outnumber Rats Four to One in Restaurant Inspections

Every restaurant operator knows which pest ends up in the news. The inspection record says the pest most likely to cost you a violation is the one nobody writes about, and the one most often treated as a cosmetic nuisance rather than a sanitation failure.

What inspectors actually cite

New York food businesses inspected between 1 January 2024 and the data pull, 27,050 in total. A business is counted once per category however many times it was cited.

Two things stand out. The largest single category is not an animal at all: 45.3 per cent of inspected businesses were cited for conditions that attract pests, which covers accessible waste, gaps, standing water and food debris. That is the category an operator can fix without a treatment programme, and the one most within their control.

The second is the gap between perception and record. Rats dominate city pest politics and sit bottom of this table at 6.5 per cent. Flies sit nearly four times higher. If you are running a kitchen and optimising for the thing most likely to generate a violation, flies and sanitation beat rodents on the arithmetic.

One caveat that cuts in the other direction: a rat citation is a more serious finding than a fly citation, and the consequences of a rodent problem for a food business are larger. Frequency and severity are different measures, and this table is frequency.

The seasonality is the operational finding

Fly citations run from 15.7 per 1,000 citations in March to 60.1 in August, and stay above 50 from July through November. We normalised by all citations issued in the same month, so this is not an artefact of inspectors simply working more in summer.

The shape matters more than the peak. The rise begins in May and June, a month or more before most operators think of it as fly season, and the decline is slow: November still runs at 57.4, higher than June. A fly programme that starts in July and stops in September misses both ends of the curve.

Autumn persistence has a specific explanation. Cluster flies and other overwintering species move toward buildings as temperatures drop, and drain and small-fly breeding continues indoors regardless of what the weather is doing. For the species-level picture, see our guide to fruit flies, drain flies and gnats, which covers how to tell which small fly you have, since the breeding site differs completely between them.

Why flies are a sanitation finding, not a spraying problem

A fly in a dining room came from somewhere, and in a commercial kitchen that somewhere is almost always one of a short list: a floor drain with an organic film, a dumpster area, a mop sink, a cracked floor tile holding moisture, or a bar mat. Adult flies are the symptom; the breeding medium is the problem.

This is why the two largest categories in the table are related. Conditions conducive to pests was cited against 12,261 businesses, and those conditions are what the flies are breeding in. Treating adult flies without finding the medium produces exactly the pattern the data shows: repeated citations at the same businesses, season after season.

1. Drains first. A drain with a biofilm will produce small flies indefinitely. Enzyme or bacterial drain treatment addresses the film; a knockdown spray does not.
2. Waste handling second. Dumpster distance, lid condition, washing frequency and the drainage underneath it do more than anything applied indoors.
3. Doors third. Air curtains, self-closers and screens, maintained rather than installed and forgotten.
4. Light traps are monitoring as much as control. What accumulates in them tells you which species you have and therefore where to look.
5. Start in May. The citation curve begins climbing before the weather feels like summer.

For how this fits a commercial programme and what it costs, see our guides to restaurant pest control and commercial pricing.

It is not a neighbourhood problem

Fly citation rates run from 24.5 per cent in Manhattan to 25.8 per cent in the Bronx, with Staten Island lower at 18.5 per cent. That is a narrow spread, and the narrowness is the point: unlike rodent pressure, which varies sharply by neighbourhood, flies are close to uniform across the city.

That is consistent with flies being generated inside the premises rather than invading from outside. A kitchen’s drains and waste handling are the same problem in Tribeca as in Tremont.

Our earlier analysis of pest violations across all inspected establishments covers the wider violation picture, and the city rodent inspection data covers how often inspectors find rats on the properties they visit.

How we did this

We used the New York City restaurant inspection dataset, which records one row per violation with a code. We resolved the codes from the published violation descriptions rather than assuming them: 04K rats, 04L mice, 04M cockroaches, 04N flies, 08A conditions conducive to pests. That step matters, because matching descriptions on the word fragment “rat” also catches “temperature” and “operation” and inflates the rat count roughly thirty-fold.

Establishment counts are distinct premises identifiers, so a business cited four times for flies is counted once. The period runs from 1 January 2024 to the date of the pull. Seasonality uses citations rather than establishments, normalised against all citations issued in the same calendar month across 2024 and 2025.

Two limits. Inspection data records what an inspector found on one visit, so it understates problems that were not present that day and reflects where the city chooses to inspect. And we computed fly citation rates by cuisine type but have not published them: the differences are real but confounded by neighbourhood, building age, kitchen configuration and inspection frequency, and we could not separate those from the cuisine itself.

Frequently asked questions

What is the most common pest violation in restaurants?

Conditions conducive to pests, cited against 45.3 per cent of the 27,050 New York food businesses inspected since the start of 2024. Among actual pests, mice lead at 26.3 per cent, with flies close behind at 24.7 per cent, cockroaches at 11.2 per cent and rats at 6.5 per cent.

Are flies a health code violation?

Yes. Flies carry their own violation code in New York, cited 8,712 times since the start of 2024 across 6,675 businesses. They are cited almost four times as often as rats, which makes them one of the most likely sources of a violation in a food business.

When is fly season in a commercial kitchen?

Citations climb from May, peak in August at roughly four times the March rate, and stay elevated through November. The late persistence surprises most operators: November runs higher than June, partly because overwintering species move toward buildings in autumn and partly because indoor drain breeding continues regardless of weather.

How do you get rid of flies in a restaurant?

Find the breeding medium rather than spraying adults. In commercial kitchens that usually means floor drains with an organic biofilm, waste and dumpster areas, mop sinks, cracked tiles holding moisture, or bar mats. Enzyme or bacterial drain treatment, waste handling and door management do more than any knockdown product, and light traps are most useful for telling you which species you have.

Sources

• NYC Open Data, DOHMH New York City Restaurant Inspection Results, violation codes 04K, 04L, 04M, 04N and 08A, 2024 to 2025. data.cityofnewyork.us
• Analysis by The Pest Control Brief, October 2026.