Hornet traps on trees in Japan

Over the last few years, I've noticed hornet traps on trees at tourist attractions and locally used locations around Saitama Prefecture. The very first one I saw was a few years ago at a campsite. But I didn't actually know what it was, because there was no explanation or clues nearby. I thought it was a bird feeder! After seeing that one, I started noticing them everywhere and it didn't take long to figure it out!

Hornet traps

As you can see in the first photo, it is made out of a large pet bottle and hung from a tree. Bear in mind that the first one I saw didn't have any hornets trapped in it, so I thought it was some sort of bird feeder at first! The bottles have an attractant in them, a sap like liquid, to lure hornets in, where they become trapped. They are often placed near trees that secrete sap, which apparently attracts hornets. I wasn't entirely sure what the liquid was, and there are probably many variations of it, but I found an article on Kyodo News that explains it:

...cut holes in the side of the plastic bottle while leaving flaps of plastic that act as gates. The participants then filled the bottle with Japanese sake, grape juice, vinegar and sugar, and gave it a stir to finish the job.

The sweet and sour aroma lures the hornets inside, but once there, they cannot escape.

I can tell you from the traps I've seen, that one trap can often catch a dozen or so of hornets. There is a honey shop in Kawagoe city that displays the hornets they catch at their bee farm in jars at the shop's counter! It is fascinating to see them up close. Hornets are a very serious threat to bee farms, so these type of traps are very advantageous. It does beg the question: aren't the bees also attracted to them? Apparently not! But please do research further if you want to avoid harming bees while using a hornet trap.