Field Notes #10: Eavesdropping
- Heather McSharry, PhD
- 3 days ago
- 5 min read
Eavesdropping
On geosmin, survival, and the species listening for rain
Field Notes is where I take one idea from the episode—something that feels like a hinge point—and follow it to see what it reveals. If you want the full story, you can read or listen to the episode here.
In the Margins
The smell of rain feels personal.
It appears in poems, songs, memories, and childhood stories. Entire generations can recognize it instantly. Yet there’s something strange about treating petrichor as though it exists for us.
The scent we call petrichor is assembled from signals produced by organisms that long predate humanity. Soil bacteria, plants, and atmospheric processes were creating this chemistry for millions of years before there was anyone around to call it the smell of rain. Which raises an interesting question:
If geosmin wasn't produced for humans, who was it for?
The natural world is full of signals. Chemical messages move constantly through ecosystems, carrying information about food, danger, reproduction, habitat, and weather. Many of those signals aren't intended for us at all. We simply happen to be capable of detecting them.
Petrichor may be one of those signals.
Instead of asking why humans love the smell of rain, it may be worth asking which other species are listening.
Underlined
These are some of the organisms, besides humans, that appear to respond to geosmin or rain-associated chemical signals:
Insects
→ Many insects use environmental odors to locate food, breeding sites, or favorable habitat. Some species are attracted to geosmin, while others actively avoid it, suggesting the compound carries ecological information rather than a universal message.
Mosquitoes
→ Rainfall creates breeding habitat. Standing water, increased humidity, and changing environmental conditions all influence mosquito behavior. While mosquitoes respond to multiple cues, the approach of rain can signal opportunity.
Desert animals
→ In arid environments, rainfall can mean the difference between survival and death. Species that detect signs of distant rain may gain access to water, food, or newly favorable habitat before competitors.
Soil organisms
→ For many organisms living in soil, rainfall signals movement, reproduction, growth, and dispersal. The arrival of water transforms entire ecosystems that may have remained dormant during dry conditions.
Individually, these responses look different. Together, they suggest that the smell of rain functions as information.
What It Points To
We live inside conversations much older than ourselves.
Outbreak Watch
Updates will only include information verified through credible reporting or official public health sources.
As of mid-morning, June 17, 2026:
The Bundibugyo Ebola outbreak in the Democratic Republic of the Congo has continued to grow rapidly. As of the latest DRC Ministry of Health update cited by ECDC, 837 confirmed cases and 196 confirmed deaths have been reported, with 376 people hospitalized in isolation. Ituri Province remains the center of the outbreak, with 767 confirmed cases across 20 health zones. North Kivu has reported 67 confirmed cases across 10 health zones, and South Kivu remains at three confirmed cases.
Uganda remains at 19 confirmed cases, including two deaths. No new cases have been reported there since June 5. Of Uganda’s confirmed cases, fourteen were imported and five were associated with local transmission events, with no current evidence of broad sustained community transmission.
The response continues to face serious operational challenges, including insecurity, delayed confirmation of suspected cases, limited supplies, and community mistrust. ECDC also reported an attack on a safe burial team in Ituri and reports that five workers were taken hostage at points of entry or control after being falsely accused of spreading Ebola. WHO continues to emphasize that community engagement, contact tracing, clinical care, supplies, and cross-border preparedness remain central to the response. The outbreak is especially concerning because Bundibugyo virus currently has no approved vaccine or specific treatment.
Political controversy also continues in Kenya over the proposed U.S.-run Ebola quarantine facility in Nanyuki. Protests have centered on concerns that Kenya is being asked to accept risk on behalf of U.S. citizens exposed during the outbreak response. At least two protesters were fatally shot in earlier demonstrations, and the facility remains politically contentious.
The MV Hondius Andes hantavirus cluster remains unchanged at 13 cases and 3 deaths. I did not find a newer official update changing the case count.
Among the 18 U.S. passengers monitored after the voyage, eight had left the National Quarantine Unit in Omaha as of the most recent update, while ten remained under observation. Three former passengers completed four weeks of monitoring in Omaha and returned to their home states for two additional weeks of monitoring by local and state public health departments.
Additional cases remain possible until monitoring periods fully close, but the absence of newly reported cases continues to support the assessment that the overall public health risk remains low.
New World screwworm remains an active animal health and agricultural concern in the United States. USDA’s current status page now points readers to a screwworm dashboard tracking confirmed animal and wild fly detections in the United States. The page also notes that all southern ports of entry remain closed to livestock trade.
The U.S. case count has increased since last week. Credible reporting based on federal and state updates now places the total at 12 confirmed animal cases, mostly in Texas, with one reported in New Mexico. Affected animals have included livestock and a dog. CDC continues to report that no locally acquired human infestations have been identified in the United States, and the risk to people remains low and localized to areas where infected flies may be circulating.
The larger concern remains the same: preventing New World screwworm from becoming reestablished in the United States. Larvae feed on living tissue and can severely damage livestock, wildlife, pets, and occasionally people. Even a small number of detections can trigger a large response because the agricultural and economic consequences of establishment would be significant.
Federal and state agencies continue surveillance, quarantine, sterile fly release, animal movement controls, and treatment guidance. FDA has also issued an emergency use authorization for a generic over-the-counter drug, nitenpyram, the active ingredient in the flea medication Nitenpyram, to treat New World screwworm in dogs and cats. It kills the adult flies so is not a stand-alone cure and cannot treat larval wound infestation.
Current Impact: Southern ports of entry remain closed to livestock imports, surveillance has expanded, and sterile fly release operations continue across affected areas.
Economic Impact: Most costs currently stem from containment efforts, trade restrictions, inspections, and surveillance rather than livestock losses.
Potential Impact: If New World screwworm were to become reestablished in the United States, the agricultural consequences could be substantial, affecting livestock health, productivity, animal movement, and trade.
I’ll be doing a Screwworm episode in the first week of July.
Postscript
Thank you for subscribing. 🫶
One of the most enjoyable parts of producing this week's episode was having the weather cooperate.
I set my recording equipment up on the patio for an approaching storm, hoping I might capture a little authentic rain. Instead, I ended up recording through the entire event. The storm you hear in the episode is real—from the first distant thunder and early raindrops to the gradual slowing of the rainfall as the system moved away. Also real are the cicadas, windchimes, and tropical birds.
Next week, we're closing out June's Summer Rain series with an Outbreak After Dark episode focused on one of summer's most persistent companions—and one of rain's least appreciated beneficiaries: mosquitoes. We'll follow the blood meal from the mosquito's perspective and explore the strange biology behind one of nature's most successful parasites.
Until next week,
— Heather
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