ailanthus
I took my shiny new Canon 50D out for a spin this weekend, and along the railroad tracks I found a worthy myrmecological subject: Crematogaster feeding at the swollen nectaries of an Ailanthus Tree of Heaven. Ailanthus is an introduced Asian tree that's gone weedy across much of North America. Our local ants don't seem to mind, though, it's extra snack food for them.