Helophilus fasciatus
In 3 days ~10%
Helophilus fasciatus (Walker, 1849), the narrow-headed marsh fly, is an abundant species of syrphid fly observed throughout the United States and Canada. Hoverflies can remain nearly motionless in flight. The adults are also known as flower flies for they are commonly found on flowers, from which they get both energy-giving nectar and protein-rich pollen. The larvae of this genus are associated with wet decaying organic material, particularly accumulations of decaying vegetation in ponds and mud and farmyard manure or silage. The adults of this species lays eggs on vegetation overhanging the water. The larvae hatch and drop into the water.
For terminology Speight key to genera and glossary Length, 13–15 mm (0.51–0.59 in) The male is dichoptic. The male's face is yellow and thickly yellow pollinose, with the middle line broadly shining reddish yellow to ferruginous but never black. The pile is pale yellowish. In profile, the face is concave on the upper three-fifths, convex below this, and the lower two-thirds convex receding, without distinct tubercle although the formation approaches one. The frons is narrowed above, and the upper portion is... Wikipedia →
| # | Park | Country | Daily sighting probability |
|---|---|---|---|
| 1 | Isle Royale National Park | 🇺🇸 United States | |
| 2 | Point Pelee National Park | 🇨🇦 Canada | |
| 3 | Riding Mountain National Park | 🇨🇦 Canada | |
| 4 | Acadia National Park | 🇺🇸 United States | |
| 5 | Shenandoah National Park | 🇺🇸 United States | |
| 6 | Pacific Rim National Park Reserve | 🇨🇦 Canada | |
| 7 | Great Smoky Mountains National Park | 🇺🇸 United States |
| # | City | Country | Daily sighting probability |
|---|---|---|---|
| 1 | Minneapolis [Saint Paul] | 🇺🇸 United States | |
| 2 | Boston | 🇺🇸 United States | |
| 3 | Chicago | 🇺🇸 United States | |
| 4 | Montreal | 🇨🇦 Canada | |
| 5 | New York City | 🇺🇸 United States | |
| 6 | Detroit | 🇺🇸 United States | |
| 7 | Toronto | 🇨🇦 Canada | |
| 8 | Washington | 🇺🇸 United States | |
| 9 | Vancouver | 🇨🇦 Canada | |
| 10 | Portland | 🇺🇸 United States |
Rare
Under 5% of wildlife watchers report a Narrow-Headed Marsh Fly sighting in San Francisco on a given day, based on 20 verified sightings from GBIF citizen-science data. It is the 387th most-seen of the 737 insects we can rate there. Over three days the chance rises to about 10%, if each day is a fresh chance.
Any time of year
In every month with enough records, under 5% of wildlife watchers report a Narrow-Headed Marsh Fly in San Francisco on a given day, so our monthly data shows no clear season.
Between noon and 3 pm
Across all the parks we cover, that three-hour window holds the most Narrow-Headed Marsh Fly sightings with a recorded time, and nearly all of them come between 6 am and 6 pm: it is a daytime animal.
21st of 21
Of the 21 cities where we can rate Narrow-Headed Marsh Fly sightings, San Francisco ranks 21st at under 5%. The best odds are in Minneapolis [Saint Paul] (United States, about 20%), Boston (United States, about 10%) and Chicago (United States, about 10%).
GBIF citizen-science records
It is estimated from how often the Narrow-Headed Marsh Fly is recorded against all the insects logged in San Francisco (20 verified sightings), 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.
