Candace Fallon, Senior Endangered Species Conservation Biologist
It’s a couple hours before sunset, and I’m zigzagging back and forth across a wide sandy trail behind my friend Becca, scanning the rocks and plants on either side for insects. Tiny checkerspot butterflies flit by. Common side-blotched lizards scamper across boulders, blue scales glinting in the light. A hummingbird zips past us, the crimson patch on its breast twinkling. The sun beats down from above. It must be close to 100 degrees, and I’m eager for the moment when the sun’s face will dip behind the canyon walls that surround us, providing us with a bit of relief.
We’re camped at Anza Borrego Desert State Park in southern California, about two hours east of San Diego, and we’ve arrived during an unprecedented heat wave just days before the official end of winter. The air feels torched, even though the canyon we’re hiking towards leads to a spring-fed palm oasis. As we hike, we pass multiple signs telling us to keep our distance from bighorn sheep. “Avoid coming between sheep and water sources,” they warn. “This helps reduce stress to the sheep due to scarcity of water in the desert.” I think about how hardy and resourceful you have to be to survive in the desert.
Anza Borrego is the largest state park in California. Just three weeks before our arrival, a profusion of delicate wildflowers blanketed the area, but those have faded and now it’s mostly woody shrubs and cacti leading the show—brittlebrush, cholla, beavertail, ocotillo. We aren’t really here for the flowers, though. We’ve come looking for something even more elusive—desert fireflies. In particular, Nelson’s desert firefly (Nelsonphotus aridus), which hasn’t been reported since 2005, and the short-horned glow-worm (Pterotus curticornis), which until February of this year had not been seen in over 60 years. Both species have been reported along the Borrego Palm Canyon Trail, the trail we’re now following.
Only a few records of these species exist, and only for the adult males. The adult females and larvae are undescribed for both species, although it is presumed that the females of the short-horned glow-worm are larviform, flightless, and nocturnal, based on the adult females of the related Douglas-fir glow-worm (Pterotus obscuripennis). The life history of Nelson’s desert firefly is even less understood, and we aren’t sure if the species is diurnal or nocturnal, although though at least one male has been observed during the day.
The trail winds up the canyon, eventually crossing the creek bed, which is dry downstream of us but has water upstream all the way to the oasis. We spend extra time around this area, hoping the moisture has kept conditions amenable for fireflies, and although we find a number of other beetles, the fireflies elude us. We enjoy sunset from a huge rock surrounded by California fan palms and once it’s dark we head back down the trail, hoping to see some evidence of glow-worms along the path. California tree frogs spring out ahead of us, croaking wildly, their calls reminiscent of tiny ducks. Although we don’t see a single glow, we are treated to nearly a dozen scorpions fluorescing bright blue-green in the beam of my UV flashlight.
Early the next morning we try again on the off chance Nelson’s desert firefly is out like it was a month prior, but again we strike out. By 10:00am it is already reaching 98 degrees. I wonder if it’s too hot, although it’s hard to know with such a short window, and I’ve found other desert fireflies in similar temperatures. Could it be that these species are only active in response to rain events? The ocotillo we’ve passed have all been flush with green leaves, indicating recent rainstorms, but I’m not sure how many days have passed. As we pack up camp and get ready to move on to another part of the park, I resolve to come back again with more time to explore.
Fireflies lost and found
Nelson’s desert firefly isn’t the only species that’s seemingly vanished from the landscape. Across the United States and Canada, dozens of firefly species are fading from the public record. Nearly 30 species haven’t been officially documented in a decade or more, leaving researchers uncertain as to whether they are in danger of extinction or simply overlooked due to cryptic life histories, low population numbers, or difficulties in identification. We call these species “lost.” Are they still out there? Clearly, there is an urgent need for targeted field surveys to look for these species. But the identifications of some of them are not straightforward, and taxonomic revisions and updated species keys would help support efforts to correctly identify and understand the diverse assemblage of firefly species that call the US and Canada home.
Until very recently, even more species were on the lost list. But targeted surveys by researchers and observations submitted by community scientists have revealed new locations for several species, bringing hope that even more will be rediscovered. This includes the Ozark spark (Photinus tenuicinctus) and the Chiricahua glow-worm (Microphotus chiricahuae), species that had not been reported since the early 2000s. In June 2025 a Firefly Atlas participant revisited a site in Arkansas where the species had been collected in 1964 and found a thriving population. Two additional populations were identified nearby. Similarly, two iNaturalist observations in 2021 and 2023 put the Chiricahua glow-worm back on the map.
Help us look for lost fireflies
We need your help! The Firefly Atlas was launched to collect distribution data for firefly species across the US and Canada, with a particular focus on those that are threatened or data deficient. Lost fireflies may fall into both of these categories, but until we have more targeted surveys, we can’t be sure what their status is. To help spur rediscovery efforts, we’re launching a new campaign targeting six elusive fireflies like Nelson’s desert firefly that haven’t been seen in a decade or more:
- Nelson’s desert firefly (Nelsonphotus aridus) – California
- Florida-candle firefly (Pyractomena barberi) – Florida
- Highlands Hammock treetop flasher (Pyractomena limbicollis) – Florida
- Everglades brownwing firefly (Photuris floridana) – Florida
- Cowaselon Creek firefly (Photuris cowaseloniensis) – New York
- Crazy Horse firefly (Photuris tasunkowitcoi) – North Dakota
These fireflies should be identifiable by their physical features, locations, activity periods, and, in some cases, flash patterns. If you’re located in one of these states where they are known to occur, can you help us look for these species and report your findings to the Firefly Atlas? To learn more about each of these, including more specific details about where each species is found, check out the new Lost Species Profiles on the Atlas website.
