They came to town in swarms.

他们蜂拥来到城里。

《新英汉大辞典》

In Scotland midges attack in swarms.

在苏格兰，蚊虫会成群攻击。

youdao

There were thousands of bees in swarms in the tree.

树上有几千只成群的蜜蜂。

youdao

At the weekly IKEA romance session in Shanghai, the elderly arrive in swarms of 70 to 700 to get the free coffee offered to holders of the IKEA Family membership card.

WSJ: In China, IKEA Is a Swede Place for Senior Romance, Relaxation

Till then the males fly in biblical swarms among the treetops, serenading the fair sex.

ECONOMIST: Cicadas in Illinois

It can be a crucial source of nutrition - some crickets and locusts that migrate in vast swarms rely on eating each other to survive the journey.

BBC: Cannibal fruit flies: Lab maggots hunt one another