A bizarre phenomenon causing honeybees to exhibit zombie-like behavior is being demystified, not in a high-tech laboratory, but through the fieldwork of university students. A semester-long project for an entomology course has resulted in a peer-reviewed scientific paper, authored by undergraduates who uncovered seasonal patterns in the grisly parasitic infections that lead bees to abandon their hives and meet a strange demise.
The research, conducted by students at San Francisco State University (SFSU), provides new insights into the threat posed by a parasitic fly, Apocephalus borealis. This fly hijacks honeybees, laying eggs within their bodies and triggering erratic, nocturnal behavior before the larvae gruesomely emerge, killing the host. The students’ work reveals that infection rates are not constant, but fluctuate significantly with the seasons, peaking in late spring and correlating with specific weather conditions. Their findings underscore the vulnerability of urban bee populations and the valuable contributions that student-led research can make to ecological monitoring.
A Campus Becomes a Laboratory
The investigation began as a class project in Assistant Professor Mitzy Porras’s “General Entomology” course during the fall 2024 semester. Several undergraduate students, including Lioh Jaboeuf, who would become the study’s first author, chose to focus their efforts on the campus’s honeybee population. The project quickly evolved from a simple course requirement into a rigorous, long-term study. From September 2024 to May 2025, the student team monitored honeybees at six different sites across the SFSU campus, including pollinator gardens and areas near the science building where infected bees had been found before.
This on-campus setting provided a convenient and dynamic environment for the hands-on research Porras champions. The work culminated in a paper published in the scientific journal Insects, a significant achievement for undergraduate researchers. The project highlights a growing emphasis in higher education on providing students with practical research experience that extends beyond the traditional curriculum and contributes directly to scientific knowledge.
The Parasite’s Grisly Life Cycle
The culprit behind the zombie-like behavior is a tiny phorid fly, Apocephalus borealis. The female fly attacks a honeybee and uses a sharp ovipositor to inject her eggs into the bee’s abdomen. Once inside, the eggs hatch into maggots that feed on the bee’s muscle and organ tissues, growing for about a week while the bee is still alive. The internal trauma and the parasite’s activity are believed to trigger the host’s bizarre behavior.
Infected bees exhibit a key symptom: abandoning their hive at night, a time when honeybees are not typically active. They fly erratically, often toward light sources, where they become disoriented and walk in circles on the ground before dying. Several days after the host bee’s death, as many as 13 fly larvae emerge from the bee’s body, pushing their way out from the junction between the head and thorax, often decapitating the corpse in the process. The larvae then pupate, and fully grown adult flies emerge about 28 days later to repeat the cycle.
Seasonal Patterns of Infection
The central finding from the SFSU undergraduates’ research is the clear seasonal fluctuation in parasitism rates. By monitoring the bee populations over nine months, the students documented a distinct pattern in the prevalence of the zombie fly infection. They found that infection rates peaked in May, when approximately 50% of the bees they collected were parasitized.
Furthermore, the students’ data analysis revealed a strong correlation between these infection rates and environmental conditions. The highest rates of parasitism were closely linked to periods of warmer temperatures and lower humidity. This discovery provides crucial insight for beekeepers and conservationists, suggesting that the threat from this parasite is not uniform throughout the year but intensifies under specific, predictable weather patterns. According to Professor Porras, this study reinforces the necessity of long-term, seasonally informed monitoring of urban bee populations to better understand and protect the pollinators vital to city ecosystems.
From Accidental Discovery to Citizen Science
The investigation into this parasitic relationship began with an accidental discovery by SFSU professor John Hafernik. After collecting some dead bees from his campus to feed a pet praying mantis, he forgot them in a vial, only to find later that fly pupae had emerged from their bodies. This startling observation led to a broader investigation. Hafernik and his students found that the fly, previously known to parasitize bumblebees, was now widely infecting honeybees in the San Francisco Bay Area, with one study finding that 77% of hives sampled were infected.
To determine how widespread the phenomenon was, Hafernik’s lab launched a citizen science project called ZomBee Watch. This program enlists the public to help track the parasite’s geographical spread. Volunteers build simple light traps to attract and collect disoriented bees at night, monitor them for emerging fly larvae, and report their findings online. The project has been highly successful, with citizen scientists confirming the presence of zombie bees across the Pacific Northwest, the southern and eastern United States, and into Canada.
Implications for Urban Pollinators
Honeybees are essential for pollinating plants in urban environments, from community gardens to backyard fruit trees. The spread of the Apocephalus borealis parasite represents yet another threat to these critical pollinators, which already face challenges from habitat loss, pesticides, and climate change. Understanding the dynamics of this host-parasite relationship is crucial for assessing the overall health of honeybee colonies, especially in dense urban settings where hives may be in close proximity.
The research conducted by the SFSU undergraduates provides a vital piece of this puzzle, demonstrating that cities can serve as living laboratories for impactful ecological studies. By identifying the seasonal and climatic drivers of infection, their work can help inform more effective monitoring and potential mitigation strategies. Moreover, the project serves as a powerful example of how hands-on research opportunities can empower students to make meaningful contributions to science, fostering the next generation of biologists and ecologists.