Relatively little information on the ecology and behavior of the chestnut lamprey is available in the primary literature. I synthesize findings from several field and laboratory studies, with an emphasis on lampreys from the St. Croix River drainage in Wisconsin and Minnesota. Spawning occurs in late May or early June, with year-toyear variability in the onset of spawning associated with differences in water temperature. After metamorphosis from the larval phase, some parasitic-phase lampreys move downstream, but others may feed parasitically in the same location where spawning and larval rearing occur. Parasitic attachments tend to occur relatively more often at night. Captive lampreys were able to attack successfully in complete darkness, but during the daytime they did not respond to visual cues when separated from hosts by a glass barrier. Like other parasitic species, chestnut lampreys tend to be size selective. Attachments tended to occur dorsally on hosts both in the laboratory and in the field. Host species in the Saint Croix River system include redhorse, northern pike, and brown trout. Much of the growth achieved during the parasitic phase occurs during the summer, but there is substantial variability in size on any given date. Although there is overlap in length, females achieve greater lengths than males. In comparison to the Manistee River and other Lake Michigan tributaries in western Michigan, the chestnut lamprey in the St. Croix River drainage has been less often perceived as a threat to trout, perhaps because of the greater availability of redhorse and other large catostomids.
