Did a Freeze-Thaw Cycle Really Keep Mosquitoes Out of Iceland?
Until October 2025, Iceland and Antarctica were the only two places on Earth with no mosquitoes at all. When three were finally caught on a farm north of Reykjavík, the story spread fast — and so did a tidy explanation for why it had taken this long: a brutal freeze-thaw winter cycle that supposedly killed mosquito eggs before they could mature. We went looking for where that explanation actually comes from and found several different, uncited stories wearing the same confident tone.
The claim
Iceland had no wild mosquitoes for as long as anyone recorded, because its unstable freeze-thaw winter climate disrupted the mosquito life cycle — killing eggs or larvae before they could mature — a mechanism commonly credited to University of Iceland biologist Gísli Már Gíslason, until this explanation was overtaken by events when mosquitoes were confirmed living wild in Iceland for the first time on record in October 2025.
Source trail
The discovery itself is not in dispute: Björn Hjaltason found three mosquitoes on a red-wine-rope moth trap at his farm in Kjós, north of Reykjavík, between October 16 and 18, 2025, and the Natural Science Institute of Iceland (Náttúrufræðistofnun Íslands) confirmed the species. From there, most coverage pivoted to the more interesting question — why had it never happened before — and reached for an explanation involving freeze-thaw cycles. Several outlets credit that explanation to Gísli Már Gíslason, a real, verifiable University of Iceland professor. At least one, Futura-Sciences, gives the identical explanation but credits it to a different, less identifiable "biologist Robert Jones" instead. A third source, a small Icelandic tourism blog, skips the freeze-thaw story entirely and offers four different unsourced theories in its place. None of the tellings we checked link to an actual paper or dataset behind any of it — including the institute's own announcement, which does not repeat the freeze-thaw explanation at all.
What's confirmed
- The October 2025 discovery, confirmed directly by the institution responsible for confirming it. The Natural Science Institute of Iceland's own news post (in Icelandic; checked 2026-08-23), fetched directly, states that Björn Hjaltason caught two female and one male mosquito on a wine-rope moth trap at the farm Kiðafelli in Kjós between October 16 and 18, 2025, and that entomologist Matthías Alfreðsson identified them as Culiseta annulata — the institute's own wording calls it the first confirmed record of a mosquito living wild in the country. The Reykjavík Grapevine's own report (checked 2026-08-23), a small independent English-language Icelandic outlet, corroborates the same species and location, citing Icelandic state broadcaster RÚV.
- Gísli Már Gíslason, the person most commonly credited with the freeze-thaw explanation, is a real, identifiable scientist — not an anonymous "expert." His own University of Iceland faculty page (checked 2026-08-23), fetched directly, confirms he has held the position of Professor of Limnology at the university's Faculty of Life and Environmental Sciences since 1988. The page lists no publications, so it does not itself confirm a specific paper behind the freeze-thaw claim — only that the person being quoted is a genuine limnologist, not an invented name.
- The institute's own explanation for how the newly found species survives Iceland's climate is narrower than the freeze-thaw story, and doesn't mention it. The same natt.is post (checked 2026-08-23) says only that Culiseta annulata "hefur aðlagað sig fremur köldu loftslagi" (has adapted to a fairly cold climate) and "lifir veturinn af á fullorðinsstigi" (survives the winter as an adult), and attributes the species' arrival to cargo shipping rather than a change in the historical mosquito-killing mechanism. It does not state, endorse, or link to any explanation for why mosquitoes were absent from Iceland before now.
What isn't
- No source we could fetch directly links to an actual study behind the freeze-thaw explanation — and attribution of the same explanation isn't even consistent. Futura-Sciences' own article (checked 2026-08-23), fetched directly, states that "biologist Robert Jones explains" the freeze-thaw mechanism — a name that appears nowhere else in our research and that we could not independently identify as a working scientist, in an article that otherwise describes Gísli Már Gíslason by his real title elsewhere in the same piece. The article cites no paper, study, or dataset for the freeze-thaw claim itself.
- A different small independent site skips freeze-thaw altogether and offers four other unsourced explanations instead. A Reykjavík-based campervan-rental company's own travel blog (checked 2026-08-23), fetched directly, lists cold temperatures, "legendary" wind speeds "of more than 35 kilometers an hour," a general "disruption in life cycle," and "the chemical composition of the Icelandic water and soil" as four separate candidate explanations — without naming a single scientist, study, or source for any of the four, and without the freeze-thaw mechanism other outlets treat as settled.
- The often-repeated 1986 story of a single mosquito caught mid-flight at Keflavík Airport can't be independently checked from here. Multiple secondary tellings describe Gíslason boarding a Greenland-to-Frankfurt flight, catching one live mosquito (most name the species as Aedes nigripes) in the cabin, and preserving it in a jar of alcohol at the Institute of Natural History — which several tellings then say was later reported lost when someone went to re-examine it. We could not locate or directly fetch a first-hand account of this story; the campervan-rental blog above places it in "the 1980s" generally, while other secondary summaries name 1986 specifically, and none of the versions we found link to an original source. It's named here because it's widely repeated, not because we verified it.
Verdict
The part of this story that matters most for accuracy is solid: Iceland's mosquito-free status really did end in October 2025, and the country's own Natural Science Institute confirmed it directly, on the record, with a named entomologist and an exact date. The part everyone adds on top — why it took until 2025 — is not one settled, sourced explanation. It's several different stories, credited inconsistently or not at all, repeated with identical confidence by outlets that don't cite each other's evidence because none of them seem to have any. The institution best placed to give the real answer had the chance, in the same post announcing the discovery, and didn't offer one.