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Observation: Photinus obscurellus
Primary Observer:
Brandie Dunn
Event Date:
2025-06-09
Status:
Verified
Survey
Site Name:
BF
Province/State:
Illinois
Event Date:
2025-06-09
Time of Day:
Night-Time
Start Time:
20:32
End Time:
22:00
Number of Observers:
2
Primary Observer:
Brandie Dunn
Additional Observers:
Michael Dunn
Target Species Genus:
unknown
Target Species Species:
unknown
Location and Habitat
Location Accuracy (meters):
0-25
Habitat Type:
Open Freshwater Wetland - Wetland Bog, fen, freshwater marsh
Habitat Type Notes:
Lovely swaths of skunk cabbage and purple angelica were noted. Cat-tails, Joe Pye Weed, Jewelweed. Oak woodland canopy increases in elevation sharply to the south. Fireflies were perched on both dried, and fresh vegetation. The oaks and elevation filtered the bright, waxing gibbous moon. Having spoken to the site steward in the past, he indicated though this site is called a Bog, it is more likely a fen.
Taken from the McHenry County Conservation District website: Not truly a bog (an acidic wetland community) but more of a graminoid fen (a grass-dominated alkaline wetland community), the site is comprised of numerous natural communities including a silt-loam prairie, calcareous seep and spring, an oak woodland and sedge meadow. The fens support calcium-loving plants like big and little bluestem and Indian grass, and provide habitat for frogs and turtles. An oak woodland also exists on site that sits a top a moraine and is dominated by red and white oaks that provide sanctuary for deer, turkeys, raccoons, possums and birds.
Elevation (meters):
825
Area Searched (hectares):
.339 hectares
Artificial Light Sources
Vehicles: Yes
Street Lights: No
Buildings: No
Street Lights: No
Buildings: No
Artificial Light Types
Sky Glow (diffuse illumination in the sky): Yes
Light Trespass (light cast on surfaces beyond its intended target): No
Glare (bright light causing visual discomfort): No
Light Trespass (light cast on surfaces beyond its intended target): No
Glare (bright light causing visual discomfort): No
Artificial Light Notes:
Only a few lights in the distance could be seen through the surrounding oak woodlands. Occasional vehicles passed by on Cherry Valley Rd. The local Village of Bull Valley has a progressive lighting ordinance that was introduced in the recent past to minimize unnecessary light pollution.
Observation
Observation Type:
Flashing
Number Observed:
50+
Genus:
Photinus
Species:
obscurellus
Observation Notes:
12 mm
Specimen Voucher Number:
Flash Behavior
First Flash Time:
21:02
Last Flash Time:
22:00
First Flash Temp (F):
59
Last Flash Temp (F):
56
Flashes in Pattern:
3
Flash Color:
Yellow
Flash Pattern Period:
3
Flash Duration:
.3
Flash Interval:
.5
Male Height Zone:
Low (0-3 ft), Moderate (3-8 ft)
Flash Location:
Flahes occured at the tops of the vegetation and some from lower to the base of the vegetation. It was less common to see individuals flying, though some did.
Male Flash Behavior:
It appeared that we observed many giving a 3 flash pattern, while some were flashing two times. There were plenty of times we just saw a single flash, which leads us to wonder about the possibility of seeing multiple species. This was our first time trying this, and we will finesse our approach as we go. Activity seemed to begin 30ish minutes after sunset, and was slowing down (but still present) by 10:00.
Female Flash Behavior:
It may be possible the female was replying with 2 flashes. We saw many double flash displays, but we didn't make the connection that it was male or female. We need to pay closer attention next week when we return.
1 thought on “Observation: Photinus obscurellus”
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Very nicely documented observation– thank you for submitting! I identified this firefly as the Murky flash-train firefly (Photinus obscurellus) based on the narrow, elongated form; the dark maroon color on the pronotum; the dark, pointed pygidium; and the quick, 2-3 pulse flash patterns. The wetland habitat of the site would also make sense for this species.
The fireflies may have been displaying from the vegetation tips rather than the air because of the cool temperatures.