What is this chrysalis/cocoon growing? Good or Bad?

Asked July 1, 2020, 4:52 PM EDT

I have a number of these 'growths' on the upper side of many leaves on a young elm in my yard. Some have a very small opening that shows a bit of fuzz. If harmful, I'll dispose of them, if healthy I will watch development impatiently to see what develops. Each growth is about 3/8" thick and 1-1/4" tall , about the size of the first 2 digits of my little finger.

All the chrysalis I have seen always hang down and this is different.

Thanks for help..

Rice County Minnesota

1 Response

Thanks for the question.

These are insect galls and have no relationship to cocoons or chrysalis. These galls are typically associated with mites or aphids. They overwinter as adults and in the spring mate and lay eggs on the surfaces of leaves. These eggs quickly hatch and emerge in very tiny immature forms. These immediately start feeding on the leaves and then something very interesting happens. They release various chemicals that trigger cell division in leaf tissue. This cell division results in the gall that you are now observing. Adults will emerge from these galls but they will be so small that I expect you would not be able to see them. These galls while perhaps unsightly will not harm your elm tree. Just ignore them. Here is some more information on these and other points:

https://extension.umn.edu/yard-and-garden-insects/insect-and-mite-galls#eriophyid-mites-1346961

http://springfieldmn.blogspot.com/2016/06/elm-leaf-finger-galls.html

Thanks for using this forum.