About 3 cm long according to the story and called Nightbug Wasp.
These are new kind of bees, specially evolved (Kirishima-style ?) to prey on yukkuri. Unlike human or other animals, they doesn't consider yukkuri as extra menu; those yukkuri are the only thing they will eat.
They can pick up baby yukkuri to bring to their nest (although non-Reimu yukkuri got picked by their hair, so they struggle and some fall to the ground. Adult yukkuri will have their skin cut for wrapping small packages of paste to bring to the nest.
Moreover, the outer wall of their nest are made from destroyed yukkuri accessories sticked together. These are mainly made from accessories of the baby and koyukkuri they catch to their nest.
The young yukkuri will be thrown into storage room, had their accessories destroyed and saw the previous captured yukkuri got cut to small pieces. Baby yukkuri's core is given to the queen to eat.
Also their sting are poisoned with capsaicin, the spicy taste of chilli.
The clan's Dosu (young Dosu, 1 metre high) sacrificed her live to make a point blank spark to the nest to save her clan.