In Search for Lost Crickets: endangered Euscyrtus japonicus

 

Euscyrtus japonicus is in the family of Gryllidae, aka crickets. It’s tiny. It has 1-1.2cm of body length. Its legs are very slender. Their wings are not sturdy enough to fly around. So, they are not good at moving. It doesn't sing, although it’s a cricket. Probably the most prominent feature of the bug is female ovipositor, the organ to lay eggs, which has almost the same length as its body. Otherwise, it’s low-key. Having said that, it’s picky for its meal. Its diet comes only from long leaves of grass families. They are not good at exploring new worlds for food with their weak wings and legs. When they have home, they make a large colony in the same bush of grass with their fellow crickets.

People from Yokohama Environmental Science Research Institute, a watch dog in charge of environmental pollution in the city, have found the bug VERY rare in the city. For that matter, in the entire Kanagawa Prefecture, meeting them is getting rarer and rarer. In the recent Red List for insects and spiders in Kanagawa (my post on September 6, 2026), they are categorized as VU = vulnerable. It’s same in Tokyo, Saitama, and Chiba. All of these prefectures including Kanagawa give Euscyrtus Japonicus the endangered status. There were lots of bitten leaves, for sure. But. Some had bite marks at its tip. The others were eaten from its edge. Unfortunately, no leaves with holes only in the middle.

Instead of crickets,
brown winged planthopper
(Pochazia shantungensis)
 is ubiquitous these days
in grass of Yokohama …
They are registered
“invasive species
that harm orchards”
 by the Plant Protection Section of
Ministry of Agriculture,
Forestry and Fisheries of Japan.

Er, well, it sounds demanding but at least around Yokohama, it seems to me grasses are abundant so the insect may not have hard times for survival. I decided to do a mini search for them in the wide expanse of grass family along the bank of Tsurumi River. The bugs leave very characteristic feeding signs if they are there. They eat only the middle of slender leaves of grass. They avoid apex, margin, and of course midvein. After their meal, the grass leaves have lots of elongated holes in both sides of midvein. Since they live en masse, the leaves of their grass “town” are supposed to have lots of holes. It must be easy to find them ... Result? Nah.

It seems to me
there are lots of meal here for the crickets.

This young Patanga japonica
has surely different table manners
 from Euscyrtus japonicus.

I simply wondered. Why? With such a lot of leaves, the cricket must be able to eat a lot. One speculation could be their be-loved field of grass which can undergo frequent disturbances in big cities of boiling planet. Take the bank of Tsurumi River. Thanks to this changing climate, sudden torrential rain over our concreted neighborhood pours water directly into the River. The grass on the bank will be inundated at once. Even if the flood is for a very short period of time, it’s enough for tiny crickets to be washed over, and extinct. Or flood control constructions. The bank receives heavy mowing at least once a year to stop overflowing into human area. Yeah, grass will come back soon but meanwhile what to eat for these picky crickets?

It’s a hard life for this inconspicuous insect. What will happen to them? I decided to search for holes when there is abundant grass in our neighborhood. The scenery looked familiar and permanent. But from Euscyrtus japonicus’ point of view, it’s turbulent surroundings. I recalled the quiet fury of these bugs’ nerds in the symposium. “Beautifully conserved nature? Look, who’s talking!?”

If you find environmental issues in Kanagawa Prefecture, please make a contact with

Kanagawa Natural Environment Conservation Center 神奈川県自然環境保全センター
657 Nanasawa, Atsugi City, 243-0121
〒243－0121　厚木市七沢657

Phone: 046-248-0323

You can send an enquiry to them by clicking the bottom line of their homepage at http://www.pref.kanagawa.jp/div/1644/

Extinctions: Preliminary result of 2026 Kanagawa Red List for Insects and Spiders

 

In June 2026, Kanagawa Prefecture preliminarily released the latest data for endangered insects and spiders in Kanagawa (; the data is retrievable from here). The reason it is “preliminary” is the announcement is only for the list of endangered ones without commentary or analysis from those researched the field. At least for now, we have only the parade of names in spread sheets. The experts, the members of Kanagawa Colloquium for Insects who made the list, said their research papers are in the process of making to be published in a year or so. We’ll know eventually the meaning of the spreadsheet in detail. Having said that, last week the experts held a public symposium in Kanagawa Prefectural Museum of Natural History to discuss their assessment. I would say, in short, their feeling from their study is quiet anger.

Looking the numbers in the list, the source of their antagonism is obvious. Previously Red List for bugs in Kanagawa was published in 2006. This is the revision for the first time in 20 years. The comparison between two lists gives us a gloomy picture. In 2006, the bugs designated “Extinction” were counted 72 species. For 2026, the number is 98. “Critically Endangered (CR)” increased its members from 21 to 139. Slightly relaxed Endangered (EN) category saw the change from 19 to 102. Those which could not be categorized CR nor EN but in dangerous condition showed their sickly growth from 112 to 262. Mr. Haruki Karube, the curator for the museum and one of the organizers of the symposium, explained this time the team employed more rigorous approaches to define the conservation status of each bug. Still, the surge in quantity is without doubt.

An egg for Green Hairstreak (Neozephyrus japonicus),
labelled 2006 EN for Kanagawa Prefecture.

In the symposium the panelists pointed out there are roughly two causes that brought the increase in numbers. One is expanding urban development. It can affect the habitat of many insects and spiders that make flat (former) agricultural areas their home. Many rice paddies and veggie fields are gone to be warehouses, logistics centers, shopping malls etc. for these 20 years in Kanagawa. The bugs for rural landscape were vanquished. Quiet anger from bug nerds ... Another reason is deer. Especially those insects and spiders dwelling deep mountains of Tanzawa are extinguishing. Voracious deer eat up the plants on the ground and rob housing (of grass and leaves), maternity hospitals (of vegetations that serve as holders of eggs), and meals (for vegetarian bugs). The veterans of bugs census lamented when they did research for 2006 version, the ridge way of Tanzawa around Mt. Hiru (ASL 1673m) 蛭ヶ岳 and Mt. Tanzawa 丹沢山 (ASL 1567m) was covered by Japanese beech and the other trees that loved ASL 1600m of rainy temperate climate. From the road, glimpsing Mt. Fuji to the west was possible only from limited number of points where the tree covers were open. In 2026, no more. Almost anywhere on the ridge of Tanzawa, Mt. Fuji shows off her majestic beauty without obstacles. The place does not have trees, or abundant greenery anymore due to the appetite of deer. Poor bugs have lost their place. Many are dying out.

I think it is Phraortes elongatus
as its antennae are as long as the half of its body.
They are in the watch list for 2026 RL of Kanagawa.

Deer themselves have a checked life. Until the 1950s, deer was a good protein for starving forest people in Kanagawa. They reduced their numbers to 300 or so in 1947. The authority made hunting female deer illegal. (Guys were spared from it until 1955.) Scientific reason of the policy was unclear and so very arbitrary birth control resulted in population explosion of deer. Their number reached its max, between 5000-13000 by estimate, in 2006. They ate forest. During the1980s, the collapse of vegetation and hence ecosystem became obvious all over Tanzawa. Soil erosion began to show signs of possible catastrophic debris flow to the downstream. In 1997, Prefectural Government started constructing deer fences here and there in mountains. In addition, from 2003 hunting deer by pros and volunteers became main coping strategy (; my post for July 14, 2017). Currently, the estimated deer population is between 1800 to 11000. Within the fences, the vegetation has returned. Is it harasho? It is promising for plants, but for bugs, it seems to me, it is not.

A scene in Tanazawa now.
Forest floor is only with plants deer do not eat.

Come to think of it, vegetables can wait until the condition is right in the form of dormant seeds underground. But animals will die out when their habitat collapses. During the 1980s, before Red List making started, probably many bugs were already starved to death. Those survived still faced problems. One of the researchers at the symposium said, “True, within deer fences many vegetables returned. But they are patchworks. Take bees. They need continuous flowers during their entire life. The flowering plants within deer fences often lack variety. They flower all at once. The forests have gap periods in terms of flowers. The seasons sans flowers are for starvation of bees. With such precarious condition, insects cannot return to Kanagawa even if they might have survived in more rural prefectures such as neighboring Shizuoka or Yamanashi.” Hmmmmmmmmmmmm.

No flower.

That’s would be a typical example of “lost biodiversity.” I hope it is not a forever thing, but the presenters for the symposium were all gloomy. One of them said “People devised their business model of tourism using the nature of Kanagawa. They innocently said Tanzawa, Hakone, and beaches of Kanagawa are so natural and attractive enough to be monetized. Heck. Do they think they know the meaning of Nature?” Well … At least for now, the best option we could choose would be to watch the changing situation and to raise our voice to stop destruction when it may occur. The organizer of the symposium concluded, “So we decided to have this occasion and make the event public. Please hold critical eyes over the habitat for bugs life and take action when your beloved beetles look in trouble. We need many eyes and voices. Citizen science could save the life of small creatures.”

If you find environmental issues in Kanagawa Prefecture, please make a contact with

Kanagawa Natural Environment Conservation Center 神奈川県自然環境保全センター

657 Nanasawa, Atsugi City, 243-0121
〒243－0121　厚木市七沢657
Phone: 046-248-0323

You can send an enquiry to them by clicking the bottom line of their homepage at http://www.pref.kanagawa.jp/div/1644/