midges, sandflies
蠓 centers on tiny biting or swarming flies: midges and sandflies. The meaning is specific to these small insect pests.
蠓 combines 虫 (insect) with 蒙, which likely contributes the sound and possibly the idea of something small or swarming. The exact historical development is uncertain.
The insect radical 虫 on the left hints at a bug, and the right side 蒙 looks like a swarm under a cover. Picture tiny midges gathering in a cloud.
For ボウ, imagine a bow (ボウ) made of swarming midges: the bow shape cues ボウ while the insects buzz around.