Glow from glow-worms

From John French, The Art of Distillation, 1651. Book 5., p133.
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To make a Luminous Water that shall give light by night.

Take the tailes of Glo-wormes, put them into a glass Stille, and distill them in Balneo, pour the said water upon more fresh tailes of Glo-worms, do this foure or five times, and thou shalt have a most Luminous Water, by which thou maist see to read in the darkest night.
Some say this Water may be made of the Skins of Herring; and for ought I know it may be profitable enough: for I have heard that a shole of Herrings comming by a ship in the night have given a great light to all the ship.
It were worth the while to know the true reason why Glo-wormes, and Herring and some other such like things should be luminuous in the night.