Beware the Serpent
A penultimate instar Paris Peacock Swallowtail Butterfly Caterpillar (Papilio paris, Papilionidae) deploys its defensive osmeterium.
The osmeterium is an eversible glandular organ positioned at the juncture of the head and thorax of Papilionidae immatures. When eversed in response to a threat, it produces a chemical odour shown to repel arthropod predators (ants, spiders, mantids). It seems logical to assume that, in conjunction with the serpent-like eyespots characteristic of final instars, the colouration and forked structure of the osmeterium rounds off the snake mimicry aimed at detering vertebrate threats.
Oddly enough, of the many many encounters I have had with Papilionid caterpillars, this has been the only time I have seen an osmeterium in use, albeit fleetingly, and this was the only capture. Personally (and proudly), I feel this may be partly because I don’t make a point of provoking or disturbing my subjects.
by Sinobug (itchydogimages) on Flickr.
Pu’er, Yunnan, China
See more Chinese caterpillars on my Flickr site HERE…