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It appears that the hind basitarsis is about the same length as the tibia. This excludes Cx. modestus in which the hind basitarsis is shorter. If the tergites are uniformly reddish-brown, with no trace of pale bands, then it might be Cx. martinii (or a very worn something else). If there are pale apical bands on the tergites, it may be Cx. territans or Cx. hortensis. If it has pale basal bands on the tergites, it's most likely Cx. pipiens or Cx. torrentium. But it's often difficult to tell from photos. Fresh specimens in good condition are usually required, though many males can be separated on genitalia characters.