Christian Bates has the right answer. One archaic meaning of the word "gauntlet" is "two parallel rows of attackers." In ancient times, "running the gauntlet" was a form of punishment in which a criminal had to run between two rows of soldiers who would attack them from both sides. https://en.wikipedia.org/wiki/Running_the_gauntlet In a cave full of snakes, any animal that enters the cave will have to "run the gauntlet" by running between many snakes that may attack at any moment.

A gauntlet in English can also mean "going through a tense threatening situation". Comes from the phrase running the gauntlet. Not sure the origin of that phrase though.

I think that this documentary is referencing the snakes who were prepared to attack their flying target on all sides. Gauntlet also refers to a fighting or attacking strategy (see the second definition for further clarity): https://www.merriam-webster.com/dictionary/gauntlet

In English there are a lot of (unusual) words for specific groups of animals. A flock of birds. A school of fish. A murder of crows. A herd of cattle. A float of crocodiles. A swarm of bees. A gaggle of geese. While some of these are used commonly - many of these are unknown and rarely used by native speakers. So it is always okay to say a group of snakes, for example. I am a native English speaker and I have never heard a group of snakes referred to as gauntlet - more common phrases are a nest of snakes, or a den of snakes. Since snakes are typically solitary creatures, I think the author has taken creative liberty here.

Most Americans probably wouldn't know gauntlet means "gloves". It is a word not typically used often but it means like "Going through a dangerous obstacle course".