Nematocampa resistaria
In 3 days ~10% in a week ~30%
Nematocampa resistaria, the filament bearer, bordered thorn or horned spanworm moth, is a moth of the family Geometridae. The species was first described by Gottlieb August Wilhelm Herrich-Schäffer in 1856. It is found in North America from British Columbia to Nova Scotia, south to Florida and California.
This species was split from the Eurasian Nematocampa limbata. The wingspan is 19–25 mm. Adults are on wing from May (or April in the deep south) to August. There is one generation in the north, two generations in the middle states and multiple generations in the southern part of the range.
Larvae feed on various deciduous and coniferous trees and shrubs, including Pseudotsuga, Tsuga, Abies, Picea, Salix, Betula papyrifera, Corylus, Fragaria and carrot (Daucus). Wikipedia →
| # | Park | Country | Daily sighting probability |
|---|---|---|---|
| 1 | Glacier National Park | 🇺🇸 United States | |
| 2 | Great Smoky Mountains National Park | 🇺🇸 United States |
| # | City | Country | Daily sighting probability |
|---|---|---|---|
| 1 | Austin | 🇺🇸 United States | |
| 2 | Toronto | 🇨🇦 Canada | |
| 3 | Minneapolis [Saint Paul] | 🇺🇸 United States | |
| 4 | Boston | 🇺🇸 United States | |
| 5 | Edmonton | 🇨🇦 Canada | |
| 6 | Chicago | 🇺🇸 United States | |
| 7 | Houston | 🇺🇸 United States | |
| 8 | Montreal | 🇨🇦 Canada | |
| 9 | New York City | 🇺🇸 United States | |
| 10 | San Antonio | 🇺🇸 United States |
With luck
About 10% of wildlife watchers report a Horned Spanworm Moth sighting in Glacier National Park on a given day, based on 9 verified sightings from GBIF citizen-science data from 2019 to 2026. It is the 134th most-seen of the 147 insects we can rate there. Over three days the chance rises to about 10%, and over a week to about 30%, if each day is a fresh chance.
August and September
In those months about 10% of wildlife watchers report a Horned Spanworm Moth in Glacier National Park on a given day, against under 5% in October to July, the lowest months.
Between 10 pm and 1 am
Across all the parks we cover, that three-hour window holds the most Horned Spanworm Moth sightings with a recorded time, and about 6 in 10 of them come between 6 pm and 6 am: it is seen both by day and at night.
Yes
Of the 2 parks where we can rate Horned Spanworm Moth sightings, Glacier National Park has the highest daily chance: about 10%. Next come Great Smoky Mountains National Park (United States, under 5%).
Same family: Geometridae
The closest relatives of the Horned Spanworm Moth that you can see in Glacier National Park (family Geometridae, Geometer Moths) are Sulphur Moth (about 10%), Brown Pine Looper Moth (about 10%) and White-Striped Black (about 10%), with each one's daily chance of a sighting.
GBIF citizen-science records
It is estimated from how often the Horned Spanworm Moth is recorded against all the insects logged in Glacier National Park (9 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.
