Tabanus sudeticus
In 3 days ~20% in a week ~40%
Tabanus sudeticus, also known as the dark giant horsefly, is a species of biting horse fly. It is the heaviest fly in Europe. The dark giant horsefly's length is around 20-25 millimeters. They have uniform dark brown eyes. Diagnostic characters include:-Upper facets of eyes distinctly larger than lower facets, and sharply delineated from them. Subcallus entirely dull and tomented, (it may have brown (areas); venter of abdomen with each segment black basally, and in a rounded median extension; black species, with yellow abdominal triangles, but little or no lateral reddish colour. Parafacials with abundant black hairs.
Dark giant horseflies are a common species to be found buzzing around cows and horses. They usually only suck blood from horses and cows, avoiding humans. They fly with a very loud buzzing. Tabanus sudeticus is found in many countries of Western Europe. It has a marked northern and western distribution; being found as far north as Southern Norway and the Western Isles of Scotland, and with an occasional record from Belarus. Wikipedia →
| # | Park | Country | Daily sighting probability |
|---|---|---|---|
| 1 | Snowdonia National Park | 🇬🇧 United Kingdom | |
| 2 | Cairngorms National Park | 🇬🇧 United Kingdom |
| # | City | Country | Daily sighting probability |
|---|---|---|---|
| 1 | Vienna | 🇦🇹 Austria |
With luck
About 10% of wildlife watchers report a Dark Giant Horse Fly sighting in Cairngorms National Park on a given day, based on 7 verified sightings from GBIF citizen-science data from 2019 to 2026. It is the 219th most-seen of the 300 insects we can rate there. Over three days the chance rises to about 20%, and over a week to about 40%, if each day is a fresh chance.
June to August
In those months about 10% of wildlife watchers report a Dark Giant Horse Fly in Cairngorms National Park on a given day, against under 5% in September to May, the lowest months.
Between 2 and 5 pm
Across all the parks we cover, that three-hour window holds the most Dark Giant Horse Fly sightings with a recorded time, and nearly all of them come between 6 am and 6 pm: it is a daytime animal.
2nd of 2
Of the 2 parks where we can rate Dark Giant Horse Fly sightings, Cairngorms National Park ranks 2nd at about 10%. The best odds are in Snowdonia National Park (United Kingdom, about 20%).
Same order: Diptera
The closest relatives of the Dark Giant Horse Fly that you can see in Cairngorms National Park (order Diptera, Flies) are Tapered Drone Fly (about 20%), Yellow-Barred Peat Hover Fly (about 20%) and Pellucid Hover Fly (about 20%), with each one's daily chance of a sighting.
GBIF citizen-science records
It is estimated from how often the Dark Giant Horse Fly is recorded against all the insects logged in Cairngorms National Park (7 verified sightings from 2019 to 2026), calibrated against known sighting rates. Figures are rounded to the nearest 10% because citizen-science data supports honest approximations, not decimals, and months with records from fewer than five people show "—". How it works.
