From a 13-yr data set that included >16,000 larvae of the Simulium arcticum complex from 241 collections at 67 sites, I determined chromosomal variation to assess whether cytotype presence and frequency at a collection site one year were similar or different the following year(s). From the larger data set, I made 36 comparisons for 19 sites that included 8,468 larvae. Cytotype presence and frequency were similar and, where analyzed, they were also similar after 5 to 9yr. Almost all instances where cytotype diversity or frequencies changed from year to year involved taxa in low numbers. Fifty of 51 comparisons of community similarity indicated that sites were more similar in subsequent years than were different sites within years. Two sets of two different sites had similar chromosomal diversity, suggesting potential physical and ecological similarity. These observations suggest that cytotypes in the S. arcticum complex exhibit stability of community assemblages and that females might be using ecological cues to choose oviposition sites. They also suggest that chromosomal observations based on collections from only one year are likely to be an accurate representation of the actual diversity present, so long as times of collection are similar and sample sizes are large.