Japanese barberry provides an exceptionally favorable environment for ticks due to the high humidity present in barberry's dense foliage. It is hypothesized that spread of barberry is correlated with the spread of Lyme disease. Tick numbers are higher in areas with thick barberry understories, as opposed to areas with controlled barberry or no barberry. In one study, 280 ± 51 adult black-legged ticks, Ixodes scapularis, were found per hectare in a barberry infected area, while only 30 ± 10 adult black-legged ticks were found per hectare in otherwise similar area with no barberry present.