Chrysops caecutiens
In 3 days ~10% in a week ~20%
Chrysops caecutiens, common name splayed deer fly, is a species of horse fly belonging to the family Tabanidae. It is also known by the colloquial name Scotch cleg. Chrysops caecutiens reaches a length of about 8.5–10 millimetres (0.33–0.39 in). The mesonotum and the scutellum are glossy black with yellow-brown hairs. The compound eyes have red and green reflections, with dark spots. The transparent wings have dark brown patches, located at the top and at the centre of each wing. The abdomen shows distinct black inverted-V marking (hence the common name of "splayed" deer fly). The legs are black, included the tibiae on the middle pair of legs. They are active from May to September.
The larvae of the splayed deer fly feed upon algae and organic matter in damp muddy soils. The adult female flies feed on mammalian blood (including on roe deer), in order for their eggs to mature properly. When they bite, they inject saliva with an anti-coagulating agent that prevents the blood from clotting. The structure of the ommatidia in the midregion of the eyes of the females may use high polarization to assist in host-finding. Adult males and females feed also on... Wikipedia →
| # | Park | Country | Daily sighting probability |
|---|---|---|---|
| 1 | Cévennes National Park | 🇫🇷 France | |
| 2 | Pyrénées National Park | 🇫🇷 France |
Rare
Under 5% of wildlife watchers report a Splayed Deer Fly sighting in Pyrénées National Park on a given day, based on 7 verified sightings from GBIF citizen-science data from 2019 to 2026. It is the 940th most-seen of the 1277 insects we can rate there. Over three days the chance rises to about 10%, and over a week to about 20%, if each day is a fresh chance.
June
In that month about 10% of wildlife watchers report a Splayed Deer Fly in Pyrénées National Park on a given day, against under 5% in July to May, the lowest months.
Between 3 and 6 pm
Across all the parks we cover, that three-hour window holds the most Splayed Deer Fly sightings with a recorded time, and about 9 in 10 of them come between 6 am and 6 pm: it is a daytime animal.
Among the best
Of the 2 parks where we can rate Splayed Deer Fly sightings, Pyrénées National Park ranks 2nd at under 5%, level with the leaders once rounded. The best odds are in Cévennes National Park (France, under 5%).
GBIF citizen-science records
It is estimated from how often the Splayed Deer Fly is recorded against all the insects logged in Pyrénées 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.
