Straggling and core 17-year broods

 Brood II  emerges four years before  Brood VI ;  Brood VI  emerges four years before  Brood X ;  Brood X  emerges four years before  Brood XIV , and  Brood XIV  emerges four years before  Brood I . These broods are also in close contact in some parts of their ranges. Thus,  stragglers  from any of these broods are of interest because they can cause gene flow among these broods. From a practical perspective,  stragglers  from any of these broods complicate mapping efforts, because populations may be difficult to assign to a brood. Some  straggling  emergences are easily identified as such, since they involve only small numbers of cicadas. Others are less easily interpreted, and the difficulty may be compounded by the problem of “shadow brooding” in which repeated instances of straggling resupply populations of  stragglers  that are on the verge of becoming self-sustaining.

Use this map to explore the boundaries of 17-year broods linked by  straggling . Filled symbols represent presence records, and open symbols represent absence records. Note that overlap between the broods is generally quite small... but since the broods are so close together, it's easy to see how  stragglers  cause confusion.

 Literature