OSAKA, May 23 (News On Japan) - A massive outbreak of insects is causing serious problems at the Osaka-Kansai Expo site, prompting alarm both on the ground and online.
The unusual phenomenon began drawing attention last week when multiple social media posts described the situation as "out of control." One widely shared photo showed insects swarming a pillar of the Expo’s iconic circular roof structure, nicknamed the "Great Ring." While some visitors claimed they hadn’t noticed any insects during their visit, others reported swarms that appeared to cling in thick clusters to walls, vending machines, and elevator shafts.
A site inspection revealed large numbers of tiny, pale-winged insects gathering especially on the upper sections of the ring. Although less dense than in the most extreme social media images, the presence of insects was undeniable. In particular, the Expo venue’s wooden pillars and shaded areas were found to be heavily coated. Visitors expressed discomfort, with some saying the insects nearly got into their food while eating, and many fled from areas thick with the bugs.
The insects have been identified as chironomids, or non-biting midges, often mistaken for mosquitoes but harmless to humans. According to researchers, they typically breed in aquatic environments and do not bite. A field investigation confirmed that they were originating from water-adjacent zones within the Expo grounds, especially near the ocean-facing sections.
One hotspot of the infestation has been the upper area of the Great Ring. While the insects are less active during the day, by around 6:30 p.m., massive swarms begin to emerge. Video taken on site shows a near-panic among visitors and even security personnel, with clouds of insects visibly filling the air. The scene became so chaotic at one point that reporters could not continue filming without being engulfed.
Expert Yamamoto from Suiken Co., who has researched midges for over 20 years, visited the site and confirmed the bugs are a salt-tolerant species of chironomid, capable of surviving in brackish water. According to Yamamoto, they likely existed on Yumeshima—the artificial island housing the Expo—even before construction began. The Expo’s environment, including the large wooden structures and artificial water bodies, has unintentionally created a perfect breeding ground.
The insects are known to lay eggs in water and then emerge in large numbers at dusk to seek high perches for mating. The wooden ring, elevated above the ground and facing the ocean, acts as an ideal rest and breeding site. Yamamoto warned that unless interrupted, this cycle would repeat daily through the summer.
Although some suspected the insects were emerging from stagnant puddles, further investigation pointed to the Expo’s southern "Water Plaza"—a 3-hectare saltwater pond popular with visitors. The absence of natural predators like fish has likely allowed the chironomid larvae to thrive. Upon closer inspection, signs of larvae were found in nests along the water’s edge.
In response to the escalating problem, Osaka Governor Yoshimura announced cooperation with a private sector company to implement control measures. He stated that he had directly requested support from the head of Kosei Seiyaku, a firm expected to aid in countermeasures.
Despite the discomfort, Yamamoto emphasized that the insects are not dangerous and will not bite. However, repellents and sprays are unlikely to be effective. He advised visitors sensitive to insects to avoid outdoor areas around sunset, especially the elevated sections of the ring. He added that the outbreak may naturally subside once peak summer temperatures arrive, although a second wave could emerge in September.
For now, Expo-goers are being urged to plan accordingly and remain aware of the insect-prone times and areas to ensure a more pleasant visit.
Source: KTV NEWS
