Tabanus sudeticus
In 3 days ~40% in a week ~70%
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 |
Possible
About 20% of wildlife watchers report a Dark Giant Horse Fly sighting in Snowdonia National Park on a given day, based on 25 verified sightings from GBIF citizen-science data from 2019 to 2026. It is the 81st most-seen of the 387 insects we can rate there. Over three days the chance rises to about 40%, and over a week to about 70%, if each day is a fresh chance.
July
In that month about 30% of wildlife watchers report a Dark Giant Horse Fly in Snowdonia 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.
Yes
Of the 2 parks where we can rate Dark Giant Horse Fly sightings, Snowdonia National Park has the highest daily chance: about 20%. Next come Cairngorms National Park (United Kingdom, about 10%).
Same order: Diptera
The closest relatives of the Dark Giant Horse Fly that you can see in Snowdonia National Park (order Diptera, Flies) are Tapered Drone Fly (about 20%), Marmalade Hover Fly (about 20%) and Common Drone Fly (about 10%), 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 Snowdonia National Park (25 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.
