Those are one of the many species of puff ball fungi, they are indicating to you that your blueberry
roots are thriving.
As has been mentioned blueberries require fungi hyphae (mycelium) to get all the nutrients they need for good growth and berry production, so you are doing well.
Also, as has been mentioned, these are not edibles, so just enjoy knowing your soil is really benefiting your blue berry bush and your going to get good crops as the result.
If you have other bushes that don't have evidence of the mycelium, simply take a bit of that plant's soil and add it to the needy ones, within a short time they too will have the fungi in the soil helping the bushes out.
Redhawk