Subject: Morning Cloak Caterpillars?
Location: Saint John, NB Canada
July 30, 2014 6:40 am
I found this congregation of caterpillars on the branch of my willow tree last night. This morning they had abandoned that branch, leaving clumps of black, and had relocated to a higher branch. I am located in Saint John, NB Canada and have never encountered these before. Based on what I’ve seen on the internet, I believe they are Mourning Cloak Caterpillars but I was hoping someone could confirm that makes sense. I’m also wondering if these are dangerous and should heed any warnings. I’m not a creepy crawly fan so I haven’t gotten too close but I’ve taken a couple of photos zoomed in as much as possible.
Though you image lacks critical detail, there are enough similarities to presume these are Mourning Cloak Caterpillars. Your very descriptive account of the sighting supports that supposition as willow is a common food plant. Mourning Cloak Caterpillars frequently feed in a group, known as an aggregation, a more accepted term for a group of caterpillars than the term congregation. Mourning Cloak Caterpillars are not considered dangerous, but the spines can cause a painful prick if they are carelessly handled.