What does this mean "machine guns looked like praying mantises to me"?

Its a simile that this person is trying to explain to the reader, the person who wrote this referring to the fact that the guns looked like a small creature, this states that the fact that the guns looked like tiny insects, the reader has to read on to find out what the author is trying to explain to the reader.
You need to read on or if no more text to read, all you can say is that the author says that machine guns looks like tiny insects from their perspective.

Hope this helps!

Because anne thinks margot is jealous towards her and peters relationship.