Stonemyia tranquilla
In 3 days ~20% in a week ~30%
Stonemyia tranquilla, commonly known as the peaceful stonian horsefly, is a species of fly in the family Tabanidae. The fly is about 1.5 cm long and, unlike most other tabanid flies, does not need to suck blood to reproduce–hence the scientific name which translates to "tranquil". Wikipedia →
| # | Park | Country | Daily sighting probability |
|---|---|---|---|
| 1 | Acadia National Park | 🇺🇸 United States |
More parks will be added in future updates.
With luck
About 10% of wildlife watchers report a Stonemyia tranquilla sighting in Acadia National Park on a given day, based on 10 verified sightings from GBIF citizen-science data from 2019 to 2026. It is the 202nd most-seen of the 405 insects we can rate there. Over three days the chance rises to about 20%, and over a week to about 30%, if each day is a fresh chance.
July and August
In those months about 10% of wildlife watchers report a Stonemyia tranquilla in Acadia National Park on a given day, against under 5% in September to June, the lowest months.
Between 10 am and 1 pm
Across all the parks we cover, that three-hour window holds the most Stonemyia tranquilla sightings with a recorded time, and nearly all of them come between 6 am and 6 pm: it is a daytime animal.
Only Acadia National Park, in our data
Acadia National Park is the only park on Wallace's Line with enough records to rate Stonemyia tranquilla sightings: about 10% of wildlife watchers there report one on a given day.
Same order: Diptera
The closest relatives of the Stonemyia tranquilla that you can see in Acadia National Park (order Diptera, Flies) are Margined Calligrapher (about 20%), Eastern Calligrapher (about 20%) and Common Drone Fly (about 20%), with each one's daily chance of a sighting.
GBIF citizen-science records
It is estimated from how often the Stonemyia tranquilla is recorded against all the insects logged in Acadia National Park (10 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.
