If you’re quite a fat, juicy caterpillar, how do you go about not being eaten by a passing bird? There are various forms of crypsis (disguise) in caterpillars, some blend in to their background habitat very well, others mimic snakes with large false eyes.
The Viceroy butterfly larvas’ strategy is cryptic camouflage, they do very well to look like they have already been eaten, and then ejected from a height onto the leaf upon which they’re feeding!
Is it the caterpillar’s choice to look like bird poop? Not really, they don’t have any say in the matter. However they may adopt an attitude that makes them look even more like poop when they are alarmed. I saw this one turn its head to the left and form a curl as pictured below, it did the same thing later, turning to the right. I’m going to keep a look out for bird droppings and see if I can photograph any that look similar.
Strangely enough it is the many generations of birds who avoided the caterpillars who looked more like poop and ate the one’s who looked less like poop that have likely brought us now to the current situation where the Viceroy caterpillars look like bird poop.
The white and green looks thoroughly convincing to me and it is hard to imagine a less appetizing looking creature. How do the little electric blue stars and bronze-green ‘comedy breasts’ fit it to the defensive strategy, I wonder? Not a fraternity prank, so I suppose that they fit into the overall plan ‘to look unlike a caterpillar’. They are only really remarkable (and in the case of the blue stars, very beautiful) when viewed close up and very few things would be interested in closely examining something that ostensibly resembles a large squirt of bird faecal matter, certainly not birds.
Birds reduce the risk of dehydration by excreting a combined waste product of the white uric acid and the green or brown stool element. As this waste can contain diseases and harmful fungi, nothing is likely to want to investigate it too closely, if at all. Thus this is likely to be an effective disguise, particularly against bird predators.
For more information about the Viceroy’s lifestyle please see the University of Florida’s Featured Creatures page on the Viceroy as it is rather good!
All images and text copyright C. Paxton 2020