How to split string with "-" as delimiter

Question

I tried to split string using "-" as delimiter. But why this doesn't work:

> stringr::str_split("158–170", "-")
[[1]]
[1] "158–170"

> strsplit("158–170", "-")
[[1]]
[1] "158–170"

I expect the output to be vector of two strings "158" and "170".