By Cassandra Mark-Chan
The North Island lichen moth, Declana atronivea, is an endemic geometrid. As its name suggests, it is found in the North Island of Aotearoa, where it is distributed from Whangarei to Wellington. This charismatic moth has a wingspan of 4-5 cm and displays intricate black and white patterns on its forewings. The striking appearance of D. atronivea has marvelled naturalists and ecologists alike since its first discovery.Renowned New Zealand entomologist George Vernon Hudson (1898) regarded D. atronivea as a “…very handsome and conspicuous insect”, a sentiment shared with Austrian Naturalist Richard Sharell (1971), who called it “…a strikingly beautiful moth”.
A clue as to the function of such colouration is perhaps depicted in its name, the Latin nomenclature ‘atro’ meaning black and ‘nivea’ meaning snowy. As such, this species was previously called the zebra moth owing to the contrasting black and white patterns, which were regarded as being similar in function to zebra stripes, that is, to break up its outline (a camouflage mechanism called disruptive colouration). It has since been renamed the lichen moth due to its apparent behaviour of resting on lichen during the day, a substrate against which it is nearly indistinguishable (at least to us humans). This factor suggests the moth may also be utilising another camouflage tactic called background matching, which allows it to blend into the lichen substrates. These hypotheses about the functional significance of this moth’s colouration have remained largely subjective and untested over the years; however, recent research has provided evidence that the colour patterns of D. atronivea are, in fact, adapted for both disruptive colouration and background matching (Mark et al., 2022). The wing pattern elements help to break up surface continuity, making it difficult for predators to detect the moths outline, as well as creating a visual resemblance to lichen which promotes concealment. But wait, there’s more! This species also displays rare wing pattern asymmetry; the size and shape of the pattern elements on each wing varies between and within individuals. Bilateral symmetry (having two sides that are a mirror image) is ubiquitous in nature but presents a paradox for defensive camouflage as symmetrical patterns can be a potent cue for visually searching predators. Declana atronivea has somehow found a way to circumvent this and develop asymmetrical pattern elements which actually function to enhance the protective value of their camouflage. All in all, this unique New Zealand moth presents a trifecta of antipredator defence.
A side note on some crazy caterpillars
If you think these moths are interesting, wait until you see the caterpillars! Like the adult moths, the juvenile forms seem to have a combination of camouflage techniques in their arsenal. These unique looking caterpillars have a mottled brown and white appearance that, when adopting particular body postures, resembles twigs or bird-droppings. This colouration actually changes throughout the instars (caterpillar life stages) and appears to reflect shifts in their size, habitat, feeding activity, and vulnerability to predation. At all stages, the caterpillars can be found curled up on themselves or standing erect from the leaf surface. The effect of their posturing behaviour coupled with their colouration and ‘lumpy’ texture at different instars is quite remarkable and may be suggestive of camouflage through masquerade (a camouflage technique where the resemblance is to an uninteresting object of the environment, so predators fail to recognise the prey as food). Hudson (1939) noted that when the larvae rest closely appressed to the leaf, with their prolegs extended but the rest of the body curled up, they closely resemble bird droppings. Sharell (1971) found this equally intriguing, stating how, when curled up in such a position, the darker parts of the body become coiled while the white parts of the first and last segments become more prominent, such that they “look exactly like bird droppings”. He additionally observed that the caterpillars have a tendency to stand stiff and motionless from the plant, the effect of which makes them look like small branches or twigs.
Another observational account noted, quite specifically, that earlier instars resemble bird droppings when curled up on the leaves, or in some cases the dorsal tubercles might resemble the top of fruiting bodies, while the fourth and fifth instars resemble shoots of Pseudopanax plants that have been “attacked by scale insects and coated with a white fungus” (Kuschel, 1975). It is also possible that the abrupt colour division of brown to white along with the lateral lines and mottled appearance of the caterpillars may serve a disruptive function (Hudson, 1898). Lastly, Sharell (1971) further suggested that the swollen thoracic hood of the later instars might function as aposematism (warning colouration), with the false eye markings being used to frighten predators!
- Hudson, G. V. (1898). New Zealand Moths and Butterflies:(Macro-lepidoptera). London: West, Newman, & Company.
- Kuschel, G. (1975). Biogeography and Ecology in New Zealand (Monographiae biologicae; 27). Dordrecht: Springer Netherlands
- Sharell, R. (1971). New Zealand insects and their story. Auckland, New Zealand: Collins
- Mark, C.J. (2022). Multifaceted Camouflage and Rare Wing Pattern Asymmetry in the North Island Lichen Moth, Declana atronivea (PhD Thesis, School of Biological Sciences, The University of Auckland).