When Invasive Geckos Meet Modern Technology
House geckos are familiar nighttime visitors throughout much of tropical Asia and the Pacific, often seen stalking insects on walls and ceilings near artificial lights. But Common House Geckos can have a much more costly interaction with the human environment when they find their way inside electrical equipment. In a newly published study in Discover Life, Honorary Professor Hinrich Kaiser of the School of Biological Sciences at The University of Hong Kong (HKU) and Przemysław Zdunek report repeated incidents in which introduced Common House Geckos (Hemidactylus frenatus) entered outdoor air-conditioning units on the Pacific island of Saipan and were electrocuted after coming into contact with electronic circuitry. The encounters short-circuited the units’ motherboards and rendered the air conditioners inoperative. The study began with what initially appeared to be an unusual isolated incident. In March 2020, an air-conditioning unit at a residence on Saipan stopped producing cool air after having remained unused for several weeks. When a technician opened the outdoor compressor, an adult gecko was found fused to its motherboard. Replacing the circuit board restored the unit to operation. Less than three months later, the problem returned on a much larger scale. Three of four air-conditioning systems at the same residence failed simultaneously. Inspection revealed multiple dead geckos on each of the three motherboards—seven animals in total, including two egg-bearing females. Once again, replacement of the damaged circuit boards restored the units. “What initially looked like a bizarre one-off event suddenly became something much more interesting,” Professor Kaiser said. “We had geckos repeatedly entering air conditioners, dying on the electronics, and taking expensive equipment with them. That made us wonder how widespread this interaction between animals and technology might actually be.” Why would a gecko enter an air conditioner? The answer may lie in the same characteristics that have made house geckos highly successful at living alongside humans throughout the tropics. Electronic components can remain warmer than their surroundings, providing ectothermic animals such as geckos with attractive sites for thermoregulation. Enclosed electrical equipment may also offer shelter from predators and protected locations associated with reproduction. Unfortunately for a gecko, crossing electrically charged contacts on a circuit board can transform an apparently desirable refuge into a death trap. Professor Kaiser and Zdunek therefore searched the scientific literature and other published sources for similar incidents. They identified reports from Australia, Cuba and Taiwan involving geckos damaging air conditioners, televisions, computers and other electrical equipment. Previous research in Taiwan documented repeated gecko-induced short circuits in air conditioners, while work in Cuba reported dozens of incidents involving electrical appliances. The consequences can extend beyond an inconvenient repair bill. Geckos have also been implicated in failures involving electrical meter rooms and high-voltage switchboards, raising the possibility of electrical fires and risks to people working with affected equipment. A small animal with potentially large economic consequences The problem may become increasingly relevant as air conditioning and other electronic infrastructure become more widespread in regions affected by extreme heat. “House geckos are extraordinarily successful at living alongside people,” Professor Kaiser said. “As humans install more electronic equipment in warm climates, we are also unintentionally creating more opportunities for these animals to interact with that technology.” The authors emphasise that the problem is likely to be underreported. Technicians may replace a failed circuit board without identifying the animal responsible, while appliance owners may never learn why their equipment stopped working. Preventing access may therefore be more effective than attempting to control the geckos themselves. The study discusses approaches including screening ventilation and drainage openings and sealing other entry points, while maintaining the airflow and drainage required by the equipment. The observations also illustrate a broader and less recognised consequence of biological invasions. The Common House Gecko has spread widely beyond its native range through its association with human transportation and settlements. Its impacts are generally considered in ecological terms, including interactions with native species. The new study demonstrates that successful invasive species can also have unexpected consequences for human infrastructure. “Biological invasions do not stop at the boundary between nature and technology,” Professor Kaiser said. “An animal weighing only a few grams can short-circuit an expensive piece of equipment. These interactions are easy to overlook, but multiplied across tropical cities and millions of appliances, their economic consequences could become significant.” The paper, “Air conditioning units as death traps for introduced Common House Geckos, Hemidactylus frenatus, on Saipan, Commonwealth of the Northern Mariana Islands, with a discussion of impacts,” was published in Discover Life in August 2026.
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HKU Hydrogeologists Identify Fermentation as Key Pathway for Ammonium Production Beneath the Pearl River Delta
A study led by Professor Jimmy Jiujiu JIAO from the Department of Earth and Planetary Sciences at The University of Hong Kong (HKU) and Professor Meng LI from Shenzhen University has identified microbial fermentation as the likely main pathway for ammonium production in sediments beneath the Pearl River Delta, helping to explain the region’s exceptionally high natural groundwater ammonium levels. The Pearl River Delta hosts the highest naturally occurring groundwater ammonium concentrations reported globally, making affected groundwater unsuitable for drinking without treatment. Previous studies linked this accumulation to nitrogen-rich organic matter in fine-grained sediments and restricted groundwater circulation, but the responsible microbial pathways and organisms remained unclear. By analysing sediment samples across the delta, the team identified the major microbial processes involved and showed how sediment depth, age and salinity shape microbial communities and ammonium-producing pathways. The findings were recently published in the journal Nature Communications. Figure 1: Artist’s impression of ammonium accumulation beneath the Pearl River Delta. The illustration shows terrestrial, transitional, and marine depositional zones, where microbial fermentation is the likely dominant pathway for ammonium production. The illustration was created based on the study’s findings and is not drawn to scale. Fermentation Identified as the Main Pathway for Ammonium Production The researchers combined geochemical and metagenomic analyses of 36 sediment samples collected from three boreholes spanning different depths. The samples covered approximately 13,000 years of geological history and represented terrestrial-dominated, transitional and marine-dominated depositional environments. By analysing microbial genetic material preserved in the sediments, the team reconstructed 770 representative metagenome-assembled genomes (MAGs), providing detailed insights into the microorganisms present and their potential metabolic functions. Microbial communities and ammonium-related metabolic potential varied significantly along the land–sea gradient. Bacteria showed greater metabolic flexibility across different sediment conditions, which may help explain these shifts, while archaea tended to retain more conserved functional traits. The team found that fermentation-related genes were the most abundant across all three depositional zones, suggesting that fermentation is likely the primary microbial pathway for ammonium production. The abundance of these genes declined with sediment depth and age as readily degradable organic matter became depleted, leaving fewer substrates for microbial fermentation and ammonium production. This accumulation was particularly pronounced in the marine-dominated zone, where fine-grained, organic-rich sediments promote microbial production while restricting groundwater flow, trapping ammonium over thousands of years. Beyond fermentation, other microbial nitrogen-processing pathways also varied across the land–sea gradient. Nitrogen occurs in several chemical forms, and in some microbial pathways, nitrate is first reduced to nitrite, which can be converted into ammonium. In the terrestrial-dominated zone, genes associated with the first step—nitrate reduction—were the second most abundant. In the more saline transitional and marine-dominated zones, genes associated with the second step—the direct conversion of nitrite into ammonium—became more prominent. These differences suggest that salinity and the availability of nitrate and nitrite influence how ammonium is produced in different depositional environments. Among the bacteria identified, the marine-associated genus Brevirhabdus emerged as a potentially important contributor to ammonium cycling. Likely a legacy of past marine depositional conditions, it carries genes involved in fermentation and the conversion of nitrite into ammonium, suggesting that ancient depositional environments may continue to shape present-day groundwater chemistry. Professor Jimmy Jiao said, “Our findings move beyond the general understanding that buried organic matter is the source of ammonium. We have identified the microbial pathways and organisms that are likely responsible for producing it and shown how these processes vary across sediments formed under different environmental conditions.” Implications for Groundwater Management By linking depositional history, hydrogeochemistry and microbial function, the study provides a framework for understanding ammonium accumulation in delta regions worldwide. The findings may help identify vulnerable areas and improve groundwater assessment, monitoring and treatment planning in densely populated delta regions. Dr Meiqing LU, first author of the paper, completed her doctoral training under Professor Jimmy Jiao at HKU before joining Professor Meng Li’s group at Shenzhen University as a postdoctoral researcher. Professor Jiao and Professor Li are the co-corresponding authors of the study. The research also involved scientists from the Southern University of Science and Technology, the Hong Kong University of Science and Technology, and East China Normal University. This research was supported by the National Natural Science Foundation of China, the Guangdong–Hong Kong Joint Laboratory for Soil and Groundwater Pollution Control, the Guangdong Provincial Key Laboratory for Soil and Groundwater Pollution Control, the Guangdong Major Project of Basic and Applied Basic Research, and the Shenzhen Science and Technology Program, among other funding sources. Figure 2: Conceptual model of historical depositional processes, biogeochemical zonation, and microbial ammonium metabolism. Image credit: Adapted from Lu et al., Nature Communications (2026). For details of the research, please refer to the paper “Microbial Drivers of Ammonium Accumulation in Holocene Sediments of the Pearl River Delta”, published in Nature Communications: https://doi.org/10.1038/s41467-026-72058-8
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