When people think of dangerous animals, lions, tigers, or sharks often come to mind first. However, the tiny and easily overlooked mosquito is, in fact, the animal responsible for the greatest number of human deaths each year. Amphibians, as ectothermic animals, do not produce body heat and carbon dioxide signals as conspicuously as humans and other warm-blooded animals do. Even so, many mosquitoes and other dipteran insects still feed on their blood.
Among them, one particularly fascinating group is the frog-biting midges, Corethrellidae. These small flies are close relatives of mosquitoes, but they have evolved a remarkable specialization: they feed on frogs and locate their hosts by eavesdropping on the loud advertisement calls produced by male anurans. Previous research has shown that Corethrella can act as vectors of the blood parasite Trypanosoma [1]. More recently, researchers also detected genetic material of the amphibian chytrid fungus Batrachochytrium dendrobatidis and ranaviruses on the bodies of Corethrella midges [2]. These findings suggest that frog-biting midges may represent a hidden disease-transmission risk among amphibian populations.
Amphibian-Feeding Insects in Taiwan
Taiwan is home to 38 anuran species in seven families, including six invasive species. For a subtropical island of only about 36,000 km², this diversity is far from low. However, studies of amphibian-feeding hematophagous insects have historically focused mainly on South America, while Taiwan has received very little attention. Before 2026, the only published record from Taiwan was a short note by the well-known malaria researcher Dr. Jih-ching Lien, who reported the presence of Corethrella nippon Miyagi, 1980 on the main island of Taiwan. Unfortunately, the collection locality was described only as northern Taiwan, and the exact site can no longer be confirmed.
Recent investigations into these interspecies interactions in Taiwan were initiated in 2025 through collaborative efforts. At that time, the laboratory where I was pursuing my master's degree invited Woo-Jun Bang, a PhD candidate at Seoul National University, to visit Taiwan through the International Internship Pilot Program (IIPP) of Taiwan's National Science and Technology Council. Bang's main research focuses on Diptera, especially mosquitoes, while our laboratory works mainly on frog bioacoustics. Frog-biting midges therefore became a natural topic for collaboration.
Because frog-biting midges search for hosts by sound, Bang designed a frog-calling trap modified from a CDC mosquito trap. The trap was made with 3D-printed parts, making it easy to assemble, disassemble, and carry into the field. During our tests in Tonglin, Taichung City, we successfully recorded C. nippon, the same frog-biting midge species previously reported by Dr. Lien in Taiwan. We also collected one species of Armigeres and two species of Uranotaenia mosquitoes. Interestingly, Uranotaenia is also known as a group of frog-biting mosquitoes.
By modifying the frog advertisement calls broadcast from the trap, we also conducted a preliminary test of acoustic preference in Taiwanese Corethrella. The advertisement call that attracted the largest number of individuals belonged to Odorrana swinhoana. However, previous frog surveys from the same locality had not recorded this species. This led us to suspect that these insects may rely on particular sound frequencies to recognize frog calls, rather than being able to distinguish the calls of different frog species.
Although small in scale, this experiment confirmed that living populations of C. nippon still occur in Taiwan. We also sequenced its complete mitochondrial genome and published the results in Ecology and Evolution [3].
Insights from Citizen Science
Although we had developed a trap that could specifically collect insects attracted to frog calls, conducting a systematic survey across the entire island of Taiwan would require enormous effort. I therefore decided to try a different approach: citizen science. Using a Google Form, I collected records from active ecological communities in Taiwan, asking wildlife photographers and naturalists to submit photos and related information showing dipteran insects feeding on amphibians.
Data contributed by citizen scientists revealed new insights that had not been obtained in previous studies. In total, we obtained 31 records. These data allowed us to analyze the phenology of insect–frog interactions and build preliminary distribution models. This online survey also revealed many localities where frog-biting midges had never been recorded before. In addition, it provided the first Taiwanese records of sand flies, Phlebotominae, feeding on amphibian blood. Because we had never collected this group using frog-calling traps, we suspect that sand flies do not use frog advertisement calls as host-finding cues [4].
This study also faced two major challenges. First, most records were taken accidentally while photographers were photographing frogs. As a result, the insects themselves were often too small or unclear for detailed morphological identification, and most could only be identified to family level. Second, the total number of records was relatively low. One possible reason is that the act of photography may disturb the frog, causing the insect to fly away before it can be documented.
Despite extensive field surveys of anurans across Taiwan, direct observations of insects feeding on amphibians remain exceedingly rare in the wild. This makes it difficult to use methods commonly applied in South America, such as collecting frog-biting midges directly from the backs of frogs to study insect–host interactions [5]. Under these conditions, systematic citizen-science surveys may offer a promising and low-cost alternative.
Future Directions
Research on amphibian-feeding hematophagous insects in Taiwan is still in its early stages. However, we have already recorded Corethrella nippon biting the endangered Nidirana shyhhuangi [6], as well as other protected frog species in Taiwan. This suggests that the potential risks these insects pose to Taiwan's amphibians should not be ignored.
Our next step is to focus on the phenology, distribution, and disease-transmission risk of these insects, especially Corethrellidae. Understanding when these insects are active is important because their seasonal occurrence may overlap with the breeding seasons of different frog species. We are also preparing to use metabarcoding to test whether amphibian-feeding hematophagous insects in Taiwan carry blood parasites or other pathogens.
In addition, we are continuing to investigate the distribution of these insects across Taiwan. Dr. Lien previously left several slide-mounted Corethrella specimens collected from Orchid Island, a small island southeast of Taiwan. During an earlier visit to the National Museum of Natural Science, we found that these specimens had not been identified to species level and were already quite old. This year, we finally collected living Corethrella cf. nippon from Orchid Island. The specimens are currently preserved at National Chung Hsing University, Taichung, Taiwan, and await further identification.
These overlooked intruders may be tiny, but they open a new window into the hidden ecological networks connecting anurans, hematophagous insects, and pathogens. Continued systematic surveys and advanced molecular techniques will be vital to unraveling the complexities of these interactions, and the study of amphibian-feeding hematophagous insects in Taiwan is only just beginning.
References
- Sigl, M., Virgo, J., Grafe, U., Henske, J., Schweinsberg, M., & Eltz, T. 2025. Uninvited guests: diversity and specificity of Trypanosoma infections in frog-biting midges (Corethrella spp.). Parasites & Vectors 18: 348. https://doi.org/10.1186/s13071-025-06993-8
- Virgo, J., Sigl, M., Eltz, T., & Schweinsberg, M. 2026. Widespread detection of amphibian pathogens in frog-biting midges (Corethrellidae): implications for xenosurveillance. Biotropica 58(2): e70173. https://doi.org/10.1111/btp.70173
- Bang, W. J., You, J. Y., Bae, Y., Chuang, M.-F., & Shin, S. 2025. Preliminary study on host use and phylogenetic analysis of Corethrella nippon in Taiwan. Ecology and Evolution 15(11): e72405. https://doi.org/10.1002/ece3.72405
- You, J.-Y., & Lin, Y.-M. 2026. A preliminary study on amphibian-feeding behavior of hematophagous Diptera (Psychodidae, Culicidae, and Corethrellidae) in Taiwan based on citizen science data. Taiwanese Journal of Entomological Studies 11(2): 5–10. https://doi.org/10.5281/zenodo.19498867
- Virgo, J., Ufermann, L., Lampert, K. P., & Eltz, T. 2022. More than meets the eye: decrypting diversity reveals hidden interaction specificity between frogs and frog-biting midges. Ecological Entomology 47: 95–108. https://doi.org/10.1111/een.13095
- You, J., Wang, Y. T., & Chuang, M. F. 2026. A rare record of a midge biting Nidirana shyhhuangi Lin et al., 2025 in Taiwan. Herpetology Notes 19: 15–16.