There are many types of insect eggs that come in shades of pink ... including spiders and moths. I would think that if this were the case, however, that you would have noticed live insects as well once they had hatched, especially since you said you had noticed a significant amount of yarn being affected.
My next guess would be some type of mold or fungus ... there lots of pink varieties. Where did you get the yarn? Perhaps if you got some of your yarn second hand it was contaminated before you received it? If this is the case, I would make sure to get rid of all of the yarn that has been affected so that the mold/fungus doesn't spread further.
Whatever it is, storing your yarns in some kind of sealed container is always a good idea to keep it protected.