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Project Noah Nature School
No 100% sure but they look like a larva of some kind of ladybug.
Here is for example a larva photo of Epilachma admirabilis (sorry, I couldn't find an english name, they have 10 black spots and are quite big, for a ladybugs.)
The page is in Japanese, but if you navigate down, you will sea a picture of a larva that looks really alike to those on your photo.
http://www.insects.jp/kon-tentoutohosi.h...
To Emma:
Thanks! I didn't know about this mission :-)
To Birding For Fun:
There were three swans species, hope I'm not messing up english names: Bewick's Swan (Cygnus columbianus bewickii) - this one is pretty popular in winter in Japan, Tundra Swan (Cygnus columbines columbines) which is pretty rare and only few birds like 3 or 4 can be found with tens of the Bewick's, and as you said - Whooper Swans.
Also, there was a pretty number of pintails.
Definitely not Black tailed because of the beak (they have half pink half black as juv.) and pink legs, rather young European Herring Gull, they are pretty popular in Japan.
