Osaka Expo 2025: Why the Insect Swarms? Chironomid Control & Essential Bug Spray Tips

The “EXPO 2025 Osaka, Kansai Expo (Japan International Exposition 2025)” is being held in Yumeshima, Osaka City, for “184 days” from April 13 to October 13, 2025.

As time goes on, more and more people are talking about the Expo on social media and with their friends. On May 31, over 180,000 people visited, and even more are expected to visit in the future.

However, when thinking about a visit to the Osaka Expo, one concern that comes to mind is the problem of “a large number of insects appearing inside the Expo venue.”

Many people who have seen a lot of insects are probably worried. They might ask themselves, “Is it safe to go out?” or “What should I do if I see an insect?”

As someone who lives in Osaka, I will talk about why so many insects are showing up at “EXPO 2025 Osaka, Kansai Expo” and how to keep them away.

Why are there so many insects at the Osaka Expo?

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In May 2025, the mass emergence of insects at the “EXPO 2025 Osaka, Kansai Expo” venue was a hot topic on social media and in the media. The insect that has appeared in large numbers at the Osaka Expo venue is a type of chironomid called Cricotopus sylvestris. As of June 2025, scientists have not yet figured out what caused this mass emergence, and they are still investigating.

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.

引用：EXPO 2025

What is Cricotopus sylvestris?

Cricotopus sylvestris is a type of fly that lives in brackish water, where seawater and freshwater mix.

Chironomids are a type of fly. They look like mosquitoes, but they do not bite or sting people.

They are attracted to light and fly in large groups from dusk to night. They like clean water and usually live near lakes, streams, and other bodies of water.

When they mate, they fly together in big groups, looking like a “mosquito pillar” (kabashira)—a bunch of tiny insects all joined together to make a column. They are small, but many people find them “creepy”.

今や万博名物ユスリカ
刺しもしないし何も怖くない
一生懸命生きてる可愛い奴らですよ pic.twitter.com/HbNKLuo1iG

— kn2011 (@KNII2010) June 5, 2025

The Cricotopus sylvestris at the Osaka Expo venue are said to come from the “Sea of Connection” outside the large roof ring on the south side of the venue and the “Water Plaza” on the inside.

Experts say that the people designing the venue might not have thought enough about hydraulics and ecology. For example, they might have asked, “What would happen if we created watersides?” They say that this sudden appearance of chironomids “could have been prevented”.

The larvae of Cricotopus sylvestris live in mud and water with organic matter. As adults, they are attracted to light and human body temperature. They tend to gather around buildings and people.

The bugs tend to emerge in large numbers from May to June, and their numbers decrease in hot weather. However, many Expo visitors have reported frightening experiences due to the mass emergence of chironomids, saying things like “the bugs were too severe” and “it was a traumatic level of fear”.

Right now, a number of companies, including Earth Corporation and Fumakilla, have said they would work with insect countermeasures. The Expo Association has announced the creation of the “Chironomid and Other Insect Countermeasures Headquarters” and said they will take action quickly.

虫が嫌いな人！絶対に大阪万博行かない方がいいよ。トラウマレベルで恐怖味わうよ。pic.twitter.com/HGsOhGFyzY

— ひで2022真実を追求 (@hide_Q_) May 30, 2025

This mass insect emergence issue at “EXPO 2025 Osaka, Kansai Expo (Japan International Exposition 2025)” is problematic.

It is thought that “artificial tidal flats and drainage canals along Osaka Bay became suitable environments for chironomid breeding, causing them to multiply rapidly”. Some people online have also criticized the design and operation of the Expo.

Let’s hope for a quick fix.

Are There Concerns About Infectious Diseases? Is It Safe?

While some people on social media are worried about the risk of infectious diseases due to the mass emergence of insects, there’s no need to worry about the spread of infectious diseases caused by the Cricotopus sylvestris that have appeared in large numbers at “EXPO 2025 Osaka, Kansai Expo“.

Although Cricotopus sylvestris look like mosquitoes, they do not bite or suck blood, and there’s no proof that they spread diseases.

But they can also be annoying and stressful for people who don’t like insects.

外だけでも気持ち悪いのに 店内に こんなに多く、食べ物に入らなければいいけど 鳥肌もん🤢 pic.twitter.com/4p3Rj7W5oW

— 裕子 (@kkkfff1234k) May 24, 2025

There might also be indirect problems related to hygiene and facilities, such as dead flies clogging ventilation systems. While it is possible that carcasses could cause allergic reactions or asthma symptoms, proper insect control measures and cleaning management are necessary.

Insect Control Methods and Countermeasures Being Implemented by the Expo Association

Even though Cricotopus sylvestris are “non-biting insects”, they fly in swarms and bother visitors.

On May 26, 2025, the Expo Association created the “Chironomid and Other Insect Countermeasures Headquarters”. They took these steps to control the insects:

Earth Corporation Provides Products

Earth Corporation provided about 3,000 products to Osaka Governor Hirofumi Yoshimura. These products were called “Mushi Konai Earth” (Don’t Come Near, Bugs!). They were used because many Cricotopus sylvestris bugs had appeared at the “EXPO 2025 Osaka, Kansai Expo” venue.

You can spray “Mushi Konai Earth for Entrance and Window Glass” on entrance lights and windowpanes to keep Cricotopus sylvestris from entering. This will work for about four months. It contains a strong water-repellent component, making it suitable for outdoor use.

Also, “Osudake No-Mat Pro Premium” is expected to quickly get rid of flying Cricotopus sylvestris because the repellent spreads immediately as soon as you push it.

Earth Corporation’s products should help reduce the damage caused by Cricotopus sylvestris. The company will keep working on countermeasures through on-site inspections and other efforts.

Are Goldfish and Medaka Effective, Too?!

There are natural ways to get rid of insects like Cricotopus sylvestris, besides using chemicals. Some people suggest that adding goldfish and medaka (a type of Japanese killifish) can be effective.

Cricotopus sylvestris larvae grow in water. If you put goldfish or medaka into puddles or ponds, the larvae will eat them. This will stop the goldfish or medaka from reproducing.

Medaka are small fish that can live in small bodies of water and are easy to care for. Because of these qualities, we are thinking about adding them to our fish pond.

You can make it even more effective by getting rid of puddles and keeping the water tanks clean as part of making the environment better. Moving forward, the “Chironomid and Other Insect Countermeasures Headquarters” will lead the way in developing new ways to control insects at the Osaka Expo. This group is headed by the Expo Association.

Is Insect Repellent Spray Okay? What Can You Do Yourself?

They are slowly starting to use insect control measures at “EXPO 2025 Osaka, Kansai Expo“. While there have been fewer reports of large numbers of insects and chironomids since June, there has not yet been confirmation that the insect problem has been resolved.

If you plan to visit the Expo before the chironomid issue is fully resolved, it’s recommended that you take steps to control insects before going.

Commercial insect repellent sprays are effective for controlling insects, including the Cricotopus sylvestris that have appeared in large numbers at the Osaka Expo venue.

There’s a rumor that spray cans are not allowed at the Osaka Expo because cans are generally not allowed. However, insect repellent sprays are not considered beverages, so you can feel safe using spray types.

大阪万博　虫
缶は缶でも飲料でないので　虫除けスプレー缶はオッケーです
持っていってね♪ pic.twitter.com/T67r91tws1

— mm (@gJrw3hSY6D24963) May 21, 2025

In addition to insect repellent spray, it’s a good idea to bring other things that can help protect you from insects other than chironomids. Some examples are insect repellent rings, long-sleeved shirts and long pants, hats, and masks.

Take Insect Countermeasures and Enjoy the Osaka Expo!

The “EXPO 2025 Osaka, Kansai Expo” faced a lot of criticism because of the large number of chironomids. But, with the help of experts and companies that make insect control products, we are developing new ways to deal with this.

People often misunderstand these flies. They have emerged in large numbers, but they do not bite people. Therefore, there is no need to worry about infections or transmissible diseases.

But there’s a small chance that insect carcasses could cause allergies or asthma if they get in your eyes or mouth or stick to your clothes. So, it’s important to take steps to control any insects that might be attracted to the area.

If you don’t like bugs, it’s best to stay away from waterfront areas. Try to stick to areas with fewer insects, or visit before dusk when chironomids are more likely to appear.

Take steps to control any insects and enjoy yourself at the Osaka Expo!