[balsam]

In the comments:

“Ostrich eggs are a spider repellent (this is such common knowledge that authors may not feel a need to clarify this detail) and spiders are sacred in Islam because a spider saved Mohammad's life. As a matter of fact, the modern mosques in Istanbul also have ostrich eggs.”

Hmm, shouldn’t these facts make ostrich eggs kind of unholy? Anybody has a resolution?

[log101]

Their sacredness is not related to metaphysics, it is not originating from their existence itself. As you said it is just because one certain spider is believed to do an important thing. For example AFAIK spiders are not used as figures in Islamic Culture, they don't have semiotic meaning. So Ostrich eggs being anti-spider doesn't necessarily mean they are evil/unholy.