Subject: Big Green worm
Location: Pretoria, Gauteng, South Africa
April 13, 2014 10:29 pm
I found these guys on my lemon tree and they have now spread to most trees in my garden.
Scary looking things with a thorn on there backs, have 2 big eyes and a mouth that looks like something out of aliens.
This is the Caterpillar of a Citrus Swallowtail, Papilio demodocus, a lovely butterfly that feeds on the leaves of citrus trees while in the larval stage. All the features you describe are used as defense mechanisms by the caterpillar, which has a forked organ known as an osmeterium that is revealed and accompanied by a scent some predators might find off-putting. We believe that is the thorn you have mentioned. The eyes and mouth you mentioned are markings that might cause a predator, like a bird, to believe this is a much larger predator, like a snake, instead of a delectable morsel.