no red ( herring) worm

The R. Bachya, ( Parshas Terumah) writes, We don’t find in the
Nidvas (Donations) Hamishkan any silk. The reason for it is, for
building of the Mishkan we may not use materials that come
from  unkosher animals. (silkworms are non kosher)

תולעת שני (red wool) The dye does not come from a worm.
It comes from a red seed that has a worm in it.
(Rambam Parah Adumah 3:2 – Rashi  Yeshayahu1:18)