A large number of chironomid midges are currently present at the Expo 2025 Osaka, Kansai, Japan (hereinafter referred to as “the Expo”) Site. The following is an update on the current situation regarding the spread of chironomid midges, the measures taken so far, and how these measures will be implemented in the future.
The Japan Association for the 2025 World Exposition (hereinafter referred to as “the Association”) has conducted a survey on the insects in cooperation with a number of businesses, and has identified them as “Chironomus salinarius” (hereinafter referred to as “chironomid midges”). Chironomid midges are believed to spawn in brackish waters where freshwater and seawater mix. The Association has confirmed, based on previous on-site surveys by specialist operators, that the source of the large numbers of chironomid midges in the Expo site is the Water Plaza and the Sea of Connections.
At present, swarms of the chironomid midges are occurring particularly during the evening and night. The insects are most prevalent on the Grand Ring (Skywalk) on the south side of the Expo site and the waterside areas to the east and west of the Grand Ring. However, their swarming locations vary depending on weather conditions and they have been observed over a wide area of the Expo site.
Chironomid midges are not reported to transmit any diseases and do not sting or bite.
To date, the Association has sprayed rainwater drainage pits, etc. with a chironomid growth inhibitor, and implemented measures to prevent infestation with repellents, cleaning, and disinfection at Association facilities. In addition, the Association is supporting the use of repellents to prevent infestations, cleaning and disinfection at shops and other facilities. No growth inhibitors have been spread to the Water Plaza or the Sea of Connections.
The Association will continue to provide support for infestation countermeasures such as cleaning, disinfection, and repellents in shops and other sales facilities. In addition, on 26 May, the association set up a “Task Force on Chironomids and Related Species”, which will work with specialists to identify the source of the outbreaks and investigate effective countermeasures that also take into account human health and environmental effects.
Based on the results of the investigations, the Association will take immediate measures against the chironomid midges to ensure that visitors can enjoy a pleasant day at the Expo site.
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