I found these caterpillars yesterday feeding on Eucalyptus ficifolia
I am pretty sure they are Doratifera casta- in some areas, known as Black Slug Cup Moth.
I opted to 're-house' the caterpillars onto another eucalypt because my ficifolia is too small to accomodate a large number. The tree should cope with the few I left in situ.
2 weeks ago