Why a Xmas item.? Because it first appears (without the cobra reference) in VN's 1924 story Christmas (& later in THE GIFT). First noted by Dieter Zimmer in his "Guide to Nabokov's Butterflies and Moths 2001"

Cobra, ready to attack?

Sorry, just another moth.

Well, not just another moth.
The worlds largest moth. Detail of wing.

Attacus atlas (Linnaeus, 1758).

Family: Saturniidae
Order: Lepidoptera
Class: Insecta
Distribution: Southeast Asia.
Wingspan: 250 – 300mm.

Seeing the tips of the forewings slowly moving in the dim light between the leaves for the first time they gave me the striking impression of a cobra’s head coming out of the dark, and I moved back instinctively.

To get an impression of the whole giant moth in its habitat, please have a look into workshop.

In dense vegetation, the dramatically strong and clear markings seem to dissolve the large wing area into small particles, giving that giant moth a good chance to stay undiscovered in spite of its enormous dimensions. Once noticed, that moth is very conspicuous and looks quite frightening.

In fact, in the tropical house the moth was sitting I watched visitors passing the place without noticing anything. The only one who noticed did look a bit shocked for a moment.

The picture was taken at the Tropical House of the Gardens of Trauttmansdorff Castle near Meran, Southern Tyrol, Italy. Camera: Minolta DiMAGE 7Hi, 2560x1920, sRGB, 51mm, F/6.8, 1/180sec., ISO-100, 2005-07-06, 17:07. No tripod, flash.

Thank you for looking.