We include 399 samples spanning most of the European range of C. punctorium. Our sampling of the native range covers southwestern Russia, eastern Ukraine, Slovenia, southwestern Germany, the Iberian Peninsula, and Italy. These sites comprise the historical native range of C. punctorium. In addition, we analyze specimens from two expanding foci: one in the Baltic States Latvia and Estonia and the other in the northeastern German state Brandenburg. Expanding populations were identified based on recent reports of novel occurrences or massive expansion from previously known, isolated occurrences (Muster et al. 2008; Jonsson 2005; Krehenwinkel pers. obs.; Tallvi, pers. comm.). The Baltic populations have only been recently identified and have probably been established less than a decade ago. Brandenburg constitutes an older population, which was first recorded in the mid‐20th century (Muster et al. 2008; Jonsson 2005; Krehenwinkel pers. obs.). Specimens were sampled by hand or sweep net. Additional samples were acquired from the Senckenberg Museum of Natural History. All mature female specimens were examined under a Leica dissecting microscope, and two morphological measurements were taken using a Leica measuring eyepiece (Leica, Wetzlar, Germany): prosoma width (at its widest part) as a measure of body size, and the length of the first leg's longest segment, the femur. As leg length relates to body size, we used relative leg length as ratio of femur length and prosoma width. We took the morphological measurements for 381 specimens from the Iberian Peninsula, Italy, Slovenia, Russia, northeastern Germany, and the Baltic states. While it is easy to quantify, body size is a trait of major ecological importance (Gardner et al. 2011). Moreover, body size has been shown to rapidly evolve in range expanding arthropods (Huey et al. 2000; Krehenwinkel and Tautz 2013).