I was puzzled by the behaviour of this, and several other blue tigers, which were hovering around a Gargaloo Parsonsia eucalyptophylla vine. They were landing on the leaves and young stems, and poking out their little proboscises, apparently tasting the plant. They pumped their wings rhythmically, from fully open to fully shut, while they were doing it, and were so busy concentrating on this obviously important activity, that this one let me come withing a foot of it to take his photo. You can see that he is interested in the leaf’s central vein. (It is a “he”. You can clearly see a raised black patch on his hindwings, that marks him as male.)
Not knowing what he was doing, I asked a question on the “Bring Back Our Butterflies” website, and found that he is getting perfumed up, before going out to meet girls.
Apparently he is extracting a chemical (possible a pyrolizidine alkaloid). This is the butterfly equivalent of Aerogard - it keeps the birds away - so replenishing the store, already in their bodies as a result of their infant diet, helps keep them safe while they go out courting.
However the reason that males spend more time at this activity than females do is that the chemical is used to make a pheromone which is excreted by “hairpencil” glands on their abdomens. In the courting process they apply it to the antennae of females, thus attracting their attention to the availability of an eligible bachelor.
I find it interesting that blue tigers use Parsonsia eucalyptophylla for this purpose, even though they are only known to breed on Secamone elliptica in our area. I’ll have to keep watch for caterpillars, to see whether the vine is actually a breeding site as well.
The website I mentioned above is managed by Frank Jordan, and is a great place of find information and ask questions about butterflies.