Here Be Dragons: Dragonflies in Yokohama

Japan is an archipelago of dragonflies. The number of dragonflies identified here so far is 214. Compared to this, number of scientifically counted dragonfly species is 54 for UK, and 117 for the EU. You’ve got the idea, right? Actually, just about 70 or 80 years ago, dragonflies were found en masse in the area of JR Shinjuku Station, aka the downtown Tokyo. In misty eyes, elderly Tokyonites spoke their sweet memory of childhood, like, “You know, after school, we sneaked in the parade ground of the army in Shinjuku to hunt for dragonflies. It was so easy to catch them by Buri.” Buri? “Yeah. Pick two small stones and tie them with thread. That’s Buri. It’s like a delicate rope with weights in both sides. We threw it high in the flock of dragonflies. The thread dangled at least one dragonfly and the catch fell down to the ground. It’s difficult for the first graders to throw Buri that high. The elder kids always dominated the game …” Oh … it’s difficult now to imagine such scenery when we stand in front of skyscrapers, including Tokyo City Hall …

Orthetrum melania

Many Japanese dragonflies has their type locality here in Yokohama. It’s because Yokohama was the first large international port for Japan. The beginning was the middle of the 19th century, the time when Darwin adventured all over the globe. Many naturalists from Europe disembarked at Yokohama to enter Japan, with their insect nets. They found yet very pastoral scenery next to their hotels. Lots of dragonflies flew about above their head. I imagine if we came in such environment from the region of 117 species, every morning must have been a thrilling fiesta. They enthusiastically identified their catches to put Latin names.

Female Lyriothemis pachygastra,
 along Umeda River near Niiharu Citizen Forest
新治市民の森

Those were the days. Now, Yokohama is the second largest city in Japan. Very urban. Rice paddies once comfy home for dragonfly larva were gone. Small streams for another kind of larva become culvert to secure more space for human activity. The number of adult dragonflies inevitably dwindles. American bullfrog and Louisiana crawfish both of which were imported after the World War II to be possible foods for humans, and Pond slider that was brought in to be sold as pets, are multiplied in Yokohama’s water. They are predators for dragonfly babies. Finally, new types of neonicotinoid pesticides, allowed for usage from 2000, are killing off aquatic insects. Many dragonfly species were extinct in Yokohama, even if their registered type locality was Yokohama. Well, there is more, not only urbanization that affected life of dragonflies in Yokohama, according to Mr. Takashi Umeda 梅田孝, dragonfly expert for the Children’s Botanical Garden of Yokohama (; my post on November 4, 2016).

 

Dragonflies are delicate. Their population wildly fluctuates with environmental change. In the process of urbanization, rice paddies in Yokohama were first abandoned for cultivation. It allowed the dragonflies living in wet land to multiply for a while. Rice paddies are inherently artificial landscape where farmers control water flow. Yeah, if the original place was a wetland, abandoned rice paddies return to abandoned wetland. If paddies had water by human intervention, once they are abandoned, the place eventually returns to dry land. From rice paddies to abandoned dryland was a typical story for Yokohama. In dry former-paddies, nymphs for dragonflies cannot survive. The explosion of dragonfly population can end up with rapid extinction. Mr. Umeda who’s researching the ecosystem for dragonflies pointed out Sympetrum parvulum and Libellula quadrimaculata asahinai Selys were such species of tragic story. They became so ubiquitous during the 1980s and the 1990s. But now, they are gone. For Yokohama, there are so many other dragonfly species which are probably on the verge of extinction because the environment of rice paddies is abandoned, if not bulldozed for urbanization …

Beautiful Calopteryx atrata,
which is getting rarer and rarer in Yokohama …

Mr. Umeda said these days we can also find several tropical dragonflies in Yokohama. You may think “Ah-ha, that’s due to Global Warming!” Er, yes, and no. The ability to fly for some dragonflies is indeed phenomenal. They can move around between continents. Some dragonflies in Yokohama, like Ictinogomphus pertinax or Aciagion migratum, are considered gradually flying to the north as the climate change continues. But most tropical dragonflies identified in Yokohama are not natural travelers. Why are they here? Mr. Umeda explained that’s the story of another unintended consequences. Until some 10 years or so ago, it was fashionable for urban schools and parks to create biotopes. The purpose at that time was to provide place of education for sustainable development for city kids whose life is cut off from waterfront with aquatic lives. Good adults thought if there was no place for human kids to experience nature, money could buy it for their school backyard. Many elementary schools in Japanese cities landscaped their school garden with a man-made pond completed with transferred aquatic vegetation. Often, they were transplanted from warmer area of the planet. They carried soil from their homeland, containing eggs and seeds of foreign species. Eggs of tropical dragonflies were such new settlers. Kids of tropical dragonflies were brought from their original home without any intention to come to Yokohama. “You know? So, we are getting familiar with Ceriagrion auranticum ryukyuanum, Lestes japonicus, etc.” In a similar context, Mr. Umeda has a reservation about releasing fireflies for tourism purpose. “Well, to make fireflies happy, the event holders eventually release freshwater snails and vegetable scraps for feeding nymphs of the bug. They would start feeding carps that provide nitrogen and phosphorus from their feces. Yeah, such minerals could be good for increasing phytoplankton that are food for water snails. But, in the end, what would happen for the original ecosystem of the place? Is it a sustainable way to manage greenery?”

Sympetram risi risi

Well, humans could wreck a havoc for natural environment even with good intentions. But we can be not-so-much a troublemaker sometimes. Scientifically well-thought of maintenance job for Yokohama’s greenery could restore the eco-system gradually. Once Futatsu-ike 二ッ池, a large pond next to Shishigaya Citizen Forest 獅子ヶ谷市民の森 (; my post on June 12, 2015), was a garbage water bath because of illegal dumping. Locals, police, and the city office cleaned up the place, and now it’s a nice pond with lots of southern cattail (Typha domingensis). The last sighting for dragonfly Aeschnophlebia longistigma in Yokohama was in 1936, but they were identified once again in Futatsu-ike in 2006. These days we can find Atrocalopteryx atrata very easily in Yokohama’s water ways. During the 1960s and 70s they were considered for extinction. Now, because aquatic vegetation is returning to Yokohama’s rivers, the environment for their home is recovering and the population of Atrocalopteryx atrata is getting larger.

Futatsu-ike, early spring

And so, one day this May, Mr. Umeda called a session with us forest volunteers in the Children’s Botanical Garden to teach sustainable way to maintain aquatic environment in Yokohama. He said “Dragonflies need continuous environment. Open water surface is crucial for female dragonflies to lay eggs. Water must be clean enough for nurturing larva. Then, for dragonflies to emerge from water, they need not so tall grass along the waterway or around the pond. While some male dragonflies declare territory over certain size of open water, female dragonflies often prefer resting in a bush next to open dry space. Or, the other species spend their entire adult life within the aquatic bush of reed. They require a delicate balance between water and dryland. Our mission is to maintain such equilibrium.” Hm, OK. “So, for example, this mulberry tree is spreading its bough over the stream. It hides the water surface from the eyes of dragonflies flying above 10 to 30m high. We cut it down!” He thinned that mulberry without hesitation. Well, it’s ubiquitous mulberry … (; my post on May 28, 2021).

This mulberry must go.

“Now, look at chameleon plants, sasa bamboos, and Japanese sweet flags, along the waterway.” “Weren’t sweet flags intentionally planted here by professional landscapers?” Mr. Umeda replied. “Yes, indeed. And that’s a huge mistake of yesteryears. These glasses accelerate aridification of swampy waterside. When they wither, they add riverbed more organic matter which can eventually make the place very muddy. Water creatures often dwell in riverbed made of so-so gravelly sands and mud. The composition is very important for them to breath. Too muddy, they will suffocate. At the end of the day water flow itself is overwhelmed by the plants and dies down. No place remains for dragonfly larva to survive. The destruction of aquatic ecosystem, you know? To stop it, we need to mow them, or preferably root them out!” So, we donned long rubber boots and ventured in the stream of Children’s Recreation Park. It was a small place. The work itself was not much, to be frank. Though, as it is a popular garden, so many visitors passed by. They saw us in surprise, or sometimes with eyes of horrors. “Are you destroying the garden?” For each question, Mr. Umeda explained patiently keeping the environment sustainable is not leaving it but adding proper human intervention … Hmmmmmm. In the end, to make a place happy for dragonflies rests on the unwearied communication … Thanks to Mr. Umeda’s endeavor, dragonflies, including some rare species, of Children’s Garden and Park are maintaining their population. He is also presiding educational classes at Children’s Botanical Garden for kids and adults who love insects. If you’re interested in it, please check the calendar here.

This is the site to be cleared.

This is the runner of Japanese sweet flags to be removed.

After our work done.

Sympetrum eroticum

Yokohama Children’s Recreation Park　横浜児童遊園地
https://www.hama-midorinokyokai.or.jp/park/jidoyuen/
Yokohama Children’s Botanical Garden　横浜こども植物園
https://www.hama-midorinokyokai.or.jp/kodomo/

213 Karibacho, Hodogaya-ku, Yokohama, 240-0025

Phone: 045-741-1015