Myrmex is a Decktet version of Spider, which I wanted to be able to play even when there isn't room to spread out my double Decktet deck.
In certain situations, a legal move will appear to fail. (It is actually being undone, probably due to a bug in one of the drag-and-drop libraries used.) Workaround: you can un-undo it using the Undo button.
Undo only undoes one move; undoing again will re-do. Undo will not undo a deal.