Oh, right :D Well, a lot of them come from words that are so old that they are almost not used at all in contemporary language.
The ones that have most obvious roots:
kwiecień (April) from kwiat (flower)
lipiec (July) from lipa (the linden tree)
sierpień (August) from sierp (sickle)
listopad (November), because liście (leaves) (s)padają (fall).
wrzesień- from wrzos (heather)
październik- from paździerz (waste from producing fiber from hemp or linen)
marzec, maj - from Latin
grudzień- from "gruda" - frozen bit of soil
luty comes from word for "very cold"
czerwiec- comes from a name of insect, the same insect is a root of word "czerwony"=red
styczeń - has unknown etymology, some guess it's from "stykać" (connect, touch,) or from "tyka" (a kind of stick/pole)
Isn't czerw a worm rather than an insect?
It seems likely that earthworms of some kind could be used to make red dye.
Admittedly "worm" can sometimes refer to the larval stage of an insect but i think it would be hard to gather enough of them to dye fabric. Perhaps the month could be named after an abbundance of caterpillars, though.