The name for the knot is "Dragonfly knot" or "Tonbo Musubi" in Japanese.
I've been told that another word for "tonbo" was "katsumushi", meaning the invincible insect, hence it was a favorite symbol of strength amongst the bushi.
I also read on Bugei Tradings website
that "the Dragonfly held a special significance to the Samurai. Their seemingly tireless movement reflected the Samurai's desire to give tireless service to his feudal Lord".