
der Schwarm
swarm
A large group of animals, especially insects, birds, or fish, that move together.
Ein riesiger Schwarm Stare verdunkelte für einen Moment den Himmel.
A huge swarm of starlings darkened the sky for a moment.
swarm / crush
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swarm
A large group of animals, especially insects, birds, or fish, that move together.
Ein riesiger Schwarm Stare verdunkelte für einen Moment den Himmel.
A huge swarm of starlings darkened the sky for a moment.

crush
(Colloquial) A person one is in love with or has romantic feelings for, often secretly.
In der siebten Klasse war Thomas mein großer Schwarm.
In seventh grade, Thomas was my big crush.

swarm / crowd
(Figurative) A large, dense mass of people often moving in the same direction.
Ein Schwarm von Touristen drängte sich durch die enge Gasse zum Marktplatz.
A swarm of tourists pushed through the narrow alley toward the marketplace.
The noun 'der Schwarm' is connected with the verb 'schwärmen'. Birds or bees 'schwärmen aus' (swarm out), and you can also 'für jemanden schwärmen' (to have a crush on someone) when you are in love. This connection explains the different meanings.
Als Kind habe ich für einen berühmten Sänger geschwärmt.
As a child, I had a crush on a famous singer.
In the animal world, 'Schwarm' is used for certain groups. Typical examples are 'ein Schwarm Fische' (a school of fish), 'ein Schwarm Vögel' (a flock/swarm of birds, especially starlings), 'ein Schwarm Bienen' (a swarm of bees), or 'ein Schwarm Mücken' (a swarm of mosquitoes).
Beim Tauchen sahen wir einen bunten Schwarm Fische.
While diving, we saw a colorful school of fish.
When 'Schwarm' describes a person one is in love with, it is often used with a possessive pronoun (mein, dein, ...) or in the phrase 'einen Schwarm haben für' (to have a crush on). This meaning is colloquial.
Sie hat ihrem besten Freund nie erzählt, dass er ihr heimlicher Schwarm war.
She never told her best friend that he was her secret crush.
The use of 'Schwarm' for a crowd of people is a metaphor. It describes a large, dense group of people moving like a swarm of animals, often without a clear individual goal.
Ein Schwarm von Neugierigen hatte sich an der Unfallstelle versammelt.
A swarm of curious onlookers had gathered at the accident site.
amount / crowd
Menge neutrally refers to a large group of people. Schwarm can also mean a dense group of people, but presents their shared movement figuratively, as with animals. Menge fits when referring simply to the group; Schwarm may be more appropriate when the group seems to be moving as one.

Nach dem Konzert zog ein Schwarm von Fans zum Bahnhof.
After the concert, a swarm of fans headed toward the train station.
Nach dem Konzert bewegte sich die Menge zum Bahnhof.
After the concert, the crowd moved toward the train station.