The thimble-sized pyramids on the witch hazels are galls made by an aphid in genus Hormaphis. I’m guessing the ones I saw were H. hamamelidis.
Inside the gall is a witch-hazel cone gall aphid. She — the aphid is female — hatched from an egg a couple of months ago and irritated the host plant until it surrounded her with gall tissue. She’ll reproduce by parthenogenesis inside the cone. It will fill up with dozens of offspring, all female.
The second generation has wings. The aphids will find other witch hazels. Their offspring — the third generation in this year’s cycle — will include males. This last generation of the season reproduces sexually. The females will lay eggs in the bark of witch hazels. Those eggs will hatch next year.
But I’m guessing about the species. The aphids I saw might be H. cornu. If that’s so, they’ll go through seven generations, rather than three, this year. And they will lay eggs on river birch as well as witch hazel.
Friends who have been to Egypt tell of the feeling of wonder they experienced when they saw the pyramids. I have’t seen the big ones, but the little ones fascinate me.
• Source: The University of Georgia has some images here:
https://www.forestryimages.org/browse/subject/62381?tab=view-images
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