The file "Host_size_regression" includes the size (length, width, area) of growing (G) and non-growing (NG) adult tapeworms in piscivorous birds and mammals. Log cestode area was also converted to log cestode mass as described in Online Appendix B. Data for cestodes of piscivorous birds were taken from Ryzhikov et al. (1985), whereas data for cestodes of mammals were taken from the primary literature (references are given for these tapeworms). The average host mass for a given cestode species is the average mass of known definitive hosts (see files "Host_masses_birds.csv" and "Host_masses_mammals.csv").