Climate Change Is Redrawing the Map for the Humble Drain Fly

The drain fly is one of those insects most people have seen without ever learning its name. Clogmia albipunctata, a fuzzy little moth-like fly of the family Psychodidae, breeds in the slimy organic film that lines bathroom and kitchen drains, storm drains, and sewage treatment works across the world. Now a new modeling study published in The Science of Nature suggests that climate change is set to rearrange where this cosmopolitan, human-associated insect can live, with tropical hotspots gradually becoming less suitable even as vast new tracts of temperate and boreal Eurasia open up.

Researchers led by Shimaa Mohamed Abduljalil of Tanta University and Mohamed G. Nasser and Sara A. Alashaal of Ain Shams University assembled an unusually large evidence base for their projections: 7,244 spatially independent occurrence records for the species, drawn largely from open biodiversity repositories such as the Global Biodiversity Information Facility. That scale matters. Presence-only distribution models are notoriously sensitive to sampling bias, and a species that lives alongside humans tends to be recorded wherever entomologists happen to live. By filtering records to remove spatial autocorrelation and evaluating model performance with spatially independent cross-validation, the team aimed to distinguish genuine climatic tolerances from the footprint of human observation.

The core of the analysis is maximum entropy modeling, or MaxEnt, a widely used machine-learning approach that estimates the probability of species presence by comparing known occurrence locations against the background environment. The authors paired their occurrence data with bioclimatic variables from the WorldClim database and, after testing for collinearity, settled on five optimized predictors: annual mean temperature (BIO1), annual temperature range (BIO7), temperature of the warmest quarter (BIO10), temperature of the coldest quarter (BIO11), and annual precipitation (BIO12). The resulting model performed strongly by the field’s standard benchmarks, achieving an area under the receiver operating curve of 0.82 and a true skill statistic of 0.86, indicating that the model discriminates suitable from unsuitable habitat far better than chance.

What limits the drain fly? According to the model, two variables dominate: annual mean temperature and annual precipitation. Annual temperature range, the difference between the hottest and coldest months, acts as an important constraint in regions with extreme thermal seasonality, a signal that the species is sensitive to large temperature fluctuations rather than simply to warmth alone. Meanwhile, cold-season thermal conditions, captured by the temperature of the coldest quarter, emerge as the principal brake on poleward expansion. In other words, the drain fly’s current distribution reflects a compromise between warmth, moisture, and a limited tolerance for harsh winters, an ecophysiological profile that makes its future fortunes tightly coupled to the trajectory of greenhouse gas emissions.

To peer into that future, the team projected habitat suitability under two contrasting representative concentration pathways. RCP 2.6 represents a mitigation scenario in which emissions are substantially curbed, while RCP 8.5 represents a high-emission future with continued strong warming. Projections were made for mid-century, around 2050, and end-of-century, around 2070, using coupled model outputs from CMIP5-class climate models. This two-scenario, two-timeframe design allows the researchers to separate the range dynamics that are essentially locked in from those that depend on how aggressively the world decarbonizes.

The projected changes are strikingly uneven across the globe. Under RCP 8.5, tropical and subtropical regions, which today form the heartland of suitable drain fly habitat, show net losses as conditions there shift beyond the species’ thermal tolerance or alter its moisture requirements. The Mediterranean basin and southwestern North America are projected to lose more than 8 percent of suitable habitat by 2070. The pattern echoes a growing body of evidence that some warm-adapted species face contraction at the equatorial edge of their ranges as temperatures climb past physiological limits, even while the cold barriers at their poleward edge dissolve.

Those dissolving barriers are exactly what the model shows in temperate and boreal Eurasia. Central Asia and East Asia stand out as major winners, gaining 8.9 percent and 9.2 percent suitable habitat respectively under RCP 8.5 by 2070. Under the mitigation scenario RCP 2.6, by contrast, distributional changes remain modest. That contrast is one of the study’s clearest messages: the magnitude of future range reshuffling for this synanthropic insect depends directly on emissions choices made over the coming decades. A world that keeps warming near the low pathway keeps the drain fly’s map roughly stable; a high-warming world hands it a large new climatic frontier.

Why should anyone care about a harmless-looking fly that hovers over bathroom sinks? The public health dimension is the reason the authors frame their results as more than biogeographic curiosity. Clogmia albipunctata has been documented as a mechanical vector of pathogenic microorganisms, carrying microbes picked up in drains and sewage into human environments. Studies in nosocomial settings have isolated a range of microorganisms from these flies, and the species has been implicated in cases of myiasis, the infestation of living human or animal tissue by fly larvae. A drain fly does not bite, but its close and constant association with human dwellings, hospitals, and wastewater infrastructure makes it an efficient bridge between contaminated substrates and the spaces where people live and receive care.

The synanthropic lifestyle also amplifies the model’s predictions. Unlike wildlife species whose range shifts depend on dispersal through fragmented natural habitat, the drain fly moves with human settlement and plumbing. Because suitable urban habitat exists across a broad swath of the temperate world, climatic suitability, rather than habitat availability, is likely the main gate on its expansion. As winters warm across Central Asia, East Asia, and other high-latitude regions, the cold-season constraint that currently holds the species back may relax, allowing established urban populations to persist and spread. The study’s authors argue that their suitability maps can therefore serve as a surveillance tool, helping public health authorities and vector control programs decide where to monitor first.

Methodologically, the paper sits within a mature tradition of species distribution modeling that has transformed climate change biology over the past two decades. MaxEnt’s presence-only framework, the use of spatially filtered occurrence data, collinearity screening of predictors, and spatially independent model evaluation all reflect hard-won lessons about what makes ecological niche models reliable rather than artifacts of sampling effort. The authors acknowledge, as the field broadly does, that bioclimate envelope models capture the climatic dimension of a species’ niche but not every ecological factor, from competition to human pest control, that shapes real distributions. Still, with a dataset of more than seven thousand records and performance metrics as strong as these, the projections offer a quantitative foundation for anticipating geographic shifts in a medically relevant species.

The broader story is one of biotic homogenization in the human age. As urbanization knits the planet’s cities into a continuous web of suitable microhabitat, and as warming erases the thermal fences that once kept warm-adapted insects out of temperate latitudes, species like Clogmia albipunctata are positioned to become even more ubiquitous. Whether that future materializes gently or dramatically depends, according to these models, on which emissions pathway humanity follows. For a fly that lives in our drains, the climate choices of the next few decades will help write its itinerary.

Subject of Research: Climate-driven global range shifts of the synanthropic drain fly Clogmia albipunctata modeled with species distribution projections

Article Title: Climate change-driven range shifts in a cosmopolitan synanthropic insect: global habitat suitability modeling and projections for Clogmia albipunctata

Article References: Abduljalil, S. M., Al-Quraishy, S., Abdel-Baki, A., Salem, M. L., Aboelhadid, S. M., Awad, E. M., Nasser, M. G., & Alashaal, S. A. (2026). Climate change-driven range shifts in a cosmopolitan synanthropic insect: global habitat suitability modeling and projections for Clogmia albipunctata. The Science of Nature, 113(5), Article 121. https://doi.org/10.1007/s00114-026-02164-6

Image Credits: AI Generated

DOI: 10.1007/s00114-026-02164-6

Keywords: drain fly, Clogmia albipunctata, climate change, range shift, species distribution modeling, MaxEnt, bioclimatic variables, public health, vector, synanthropic species, RCP scenarios, habitat suitability