Asked June 13, 2016, 5:02 PM EDT

A cocoon like white material about the size of a fat pencil has appeared on a tree over the last 24 hours and 12 or 14 small butterflies flying around it, landing next to it; they appear to be tending it in some way. Can you explain? I'll try to send photo.

DuPage County Illinois

1 Response

The white material is a frothy mass of fermenting tree sap. Sometimes wild yeasts or bacteria will grow rapidly in small pockets of tree sap under the bark of trees. The pressure that builds up during fermentation causes the material to ooze out to where it can be seen. The butterflies in the picture are red admirals, a species that really loves tree sap as a food (they don't take nectar from flowers very often). They can detect it from far away when it is fermenting.