。
There's a bee buzzing around.
Literal
Bee [subject-が] one-[counter-ぴき] buzz-buzz saying
ぶんぶん is the 擬音語 (sound mimetic) for a buzzing sound — bees, flies, mosquitoes, motors. The pattern [mimetic] + いう literally 'to say [mimetic]' is a common way in Japanese to report that something is making a sound — 'a bee is saying buzz-buzz' = 'a bee is buzzing'. 1ぴき uses the counter 匹 for small animals; normally 匹 reads ひき but changes to ぴき after 1.