hedgehog
蝟 centers on the hedgehog, a small spiny mammal. The meaning is specific and does not extend to broader abstract ideas.
蝟 combines 虫 (insect/creature) with 胃, which likely provides the sound. The character was used for the hedgehog, though the exact historical development is uncertain.
The left side 虫 suggests a small creature, and the right side 胃 looks like a spiky stomach. Imagine a hedgehog as a tiny creature with a belly covered in spikes.
For イ, picture an eagle (イーグル) trying to catch a hedgehog but getting pricked: eagle -> イ, and the hedgehog's spines protect it.
swarm; throng; flock together