Reimu was a fool to engage the wasp encounter. Their size give them a +8 bonus to AC, making it impossible for Reimu to hit them without rolling a natural critical.
Then Explain how are they able to eat Bugs in the majority of the cases.
Seriously AIE, it's like saying that yukkuris don't eat mushrooms, way to many pics show them eating bugs so, to some degree, they should be able to kill them. So the potential of pest control is there if you, well, train them to make them more capable of the task.
This pic, if anything, is typical natural karma striking because the yukkuri is being a douchebag.
Yukkuris can eat insects, this is not the normal case. I'm certain they can eat bees if they catch them... but the problem is catching it unscathed. I don't really feel like the yukkuri is being a douchebag in this instance, but its funny to see it trying to argue with bees and then getting owned.
It's more of an ironic/sarcastic joke thing than justice karma. I don't think Kou was thinking too seriously about making this, it's just an amusing take run from allergies.