1In swarms; in clusters — used mimetically to describe many things or creatures gathered together.
庭に蚊がうじゃうじゃいて、外に出られない。
The yard is swarming with mosquitoes; I can't go outside.
子猫がダンボールの中でうじゃうじゃ眠っていた。
Kittens were sleeping in a cluster inside the cardboard box.
夏祭りの会場は人がうじゃうじゃいた。
People were swarming at the summer festival venue.
2Tediously; slowly — used to describe something dragging on or moving sluggishly.
彼の話は要点がなくて、うじゃうじゃ長く続いた。
His talk had no point and dragged on tediously.
古いパソコンは動きがうじゃうじゃしてイライラする。
The old PC runs sluggishly and it's frustrating.