Generalizations of the Eierlegende–Wollmilchsau

We classify a natural collection of GL(2,R)-invariant subvarieties which includes loci of double covers as well as the orbits of the Eierlegende-Wollmilchsau, Ornithorynque, and Matheus-Yoccoz surfaces. This is motivated in part by a forthcoming application to another classification result, the classification of "high rank" invariant subvarieties. We also give new examples, which negatively resolve two questions of Mirzakhani and Wright, clarify the complex geometry of Teichmuller space, and illustrate new behavior relevant to the finite blocking problem.