What do you think they are?
Exhibit
1
Duration
of Adult Life (approx. ave. max): a week
Feeding
as an adult: none
Exhibit
2
Duration
of Adult Life (approx. ave. max): two weeks
Feeding
as an adult: none
Exhibit
3
Duration
of Adult Life (approx. ave. max): a day
Feeding
as an adult: none
Exhibit
4
Duration
of Adult Life (approx. ave. max): 10 days
Feeding
as an adult: none
Exhibit
5
Duration
of Adult Life (approx. ave. max): two weeks
Feeding
as an adult: none
Exhibit
6
Duration
of Adult Life (approx. ave. max): 50 days
Feeding
as an adult: meat-eater
Exhibit 7
Duration
of Adult Life (approx. ave. max): two weeks
Feeding
as an adult: none
They are
larvae for aquatic insects all regularly found in Yodoriki River 寄沢 running through Yadoriki Water Source Forest やどりき水源林 of
Tanzawa. Their presence is a good thing for us in Kanagawa Prefecture. Japanese
Ministries of Environment and of Land, Transport and Infrastructure publish
study guides for kids to try water quality testing (; the texts are retrievable
from here and here). Both of them cite above babies of bugs to be found in the
best quality water-flows in Japan. Yadoriki River is a tributary of Sakawa River 酒匂川 that provides roughly 1/3 of water for us, the
City of Yokohama inclusive. Wonderful. One day, one of my senior Forest Instructors
went deep upstream of Yadoriki River with an ambition to collect “pure” water
from the source of the source. He reached there and found lots of these
officially designated indicator species happily wriggling in a river bed of the
transparent stream. Could he collect water for his best tea without catching
them or their excrements? He decided not to try, and returned with his empty
water bottle … A lesson learned: knowing a thing can sometimes limit your
action.
 |
| Could
you see something oblong in left corner of a plastic vessel? It’s a casing of a caddisfly larva. It collects particles of sand, glue them around its body with its excrement, and hide inside, probably dreaming for its very short adult days … FYI, We returned them after making an observation record. |
 |
| Don’t you think there is something down there in the riverbed? |
 |
| So I
tried water-proof cover for my cell-phone to take a photo inside of the stream … Couldn’t catch any clear-cut shot … but it’s an arty photo, isn’t it? |
Utility-wise,
finding them in our water source is re-assuring for sure … But after learning a
bit of their life, I felt a sort of melancholy. Those bugs spend roughly 1 year
(or 2-3 years for Protohermes grandis)
as larva, to eat voraciously underwater ... Having larva of fireflies as pets
is a hobby requires 300,000 -400,000 yen per year to purchase living pond
snails to satisfy their appetite … They then become adults one day, within few
days find their mate, lay eggs, and die. Many of them even do not eat during their
very short adult days. Latin name of Mayflies, Ephemeroptera, says everything. Ephemeral. It’s just a fact of
nature, and they don’t argue about it … How holy they are …
 |
| During
the season of firefly mating, you can of course visit the places in the evening to watch their illuminated dance. But at least in Metropolitan Tokyo area, it’s a bit congested attraction. So, I recommend you to visit the places daytime, and quietly search for the bugs resting beneath the leaves. This guy was sleeping in Niiharu 新治市民の森 this summer. |
 |
| Ditto in Yokohama’s Nature Observation Forest 横浜自然観察の森. |
One day,
in internet, I found a free fortune telling to predict my reincarnation.
According to this, after the current cycle as a human, “You’ll be an insect. At
least it won’t last long enough for you to suffer, so you should be happy about
it.” … Yes, sure, indeed. Thank you, internet. I’m now looking forward to being
a larva of crane fly in Yadoriki, inspected my junior Forest Instructors
someday, and die quickly. Oh so divine!
 |
| A
scene of Yadoriki River after heavy rain. Those larvae are surviving this … |
By the way, if you visit Yadoriki Water Source Forest on 18, 19, 25 of this month, we Forest Instructors will assist you, free of charge and all the equipment provided, to hunt larvae of water insects from Yadoriki River. (Weather permitting, of course.) Please come to the entrance gate of the forest either at 10:00 or 13:00 during the above weekend. The temperature of Yadoriki Forest is at least 3°C lower than in downtown, always.😊
If you find an environmental issues
in Tanzawa, 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/
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