Plague of flying pests adds to Osaka World Expo’s woes in Japan
Though the ‘chironomids’ do not bite or suck blood, they may cause asthma or allergic reactions, experts warn
Japan’s 2025 World Expo in Osaka has been bugged by a string of mishaps since its opening in mid-April – the latest being a plague of mosquito-like insects known as midges.
Swarms of these insects have been attracted to the wooden walls and pillars of the “Grand Ring”, a centrepiece of the expo and its main thoroughfare. Visitors have been forced to fend the flying insects off to avoid swallowing or inhaling them, raising concerns about potential health risks.
“They landed on the bread I was eating. There are so many of them around and it’s disgusting,” said Toma Masatani, a 23-year-old graduate school student visiting the expo with friends from Saitama, near Tokyo, as quoted by Kyodo news agency.
Expo organisers have identified the insects as chironomids, a species that does not bite or suck blood, according to The Japan News. However, their dead bodies can pose a health hazard: inhaling or ingesting them can trigger asthma and other allergic reactions.
“Wearing a face mask is advisable for those with asthma,” said Koichiro Kawai, a professor emeritus at Hiroshima University specialising in the species, in an interview with Kyodo.
Experts predict the infestation will persist until late autumn. The bugs are believed to have spawned in the Water Plaza, a large seawater storage area on the expo grounds, which is built on reclaimed land over a former landfill.
Nao Yamamoto, an analyst with environmental analysis company Mizuken, told The Japan News that the insects collected at the expo site belong to the Chironomus salinarius Kieffer species. These salt-tolerant midges thrive in areas where fresh and saltwater mix, with their population peaking in May and June.
“It was not this bad when I came at the end of April,” a 70-year-old woman from Osaka city who visited the event with four friends told The Japan News. “They almost got in my eyes, which was disgusting.”
To combat the infestation, expo organisers have deployed insecticides, treated rainwater-prone areas with growth inhibitors and installed insect-repellent lights.
Consultations with experts and the Environment Ministry are ongoing, while Osaka Governor Hirofumi Yoshimura has enlisted the help of Japanese insecticide manufacturer Earth Corporation.
Suffering setbacks
The midges are the latest in a string of controversies that have plagued the expo since its April 13 opening. Public frustration has mounted over issues such as long queues, a bomb scare, rogue drones, a malfunctioning subway line and fears of a methane explosion.
Even visitor behaviour has drawn criticism, with parents complaining about the lack of privacy in restrooms for toddlers, the Asahi Shimbun newspaper reported on Saturday.
Earlier, the absence of women’s restrooms at a construction site sparked public outrage following a worker’s plea to the Osaka Prefectural Government in March.
Ticket sales have also fallen short. Organisers projected 14 million admissions for the six-month event, but as of May 9, only 11 million tickets had been sold.
