Another reason might be that there are not enough nutrients in wings so the ants simply leave them.  There might be chitin but maybe its too much work to separate that from inert tissues?

That's interesting! Butterfly wings, such as those of Hebomoia glaucippe, possess toxins, so maybe this has something to do with it :-)

Another reason might be that there are not enough nutrients in wings so the ants simply leave them.  There might be chitin but maybe its too much work to separate that from inert tissues?

I would agree with the answer by Casper Vanderwoude. In the insect wings there is probably especially sclerotin, that may be indigestible for many entomophagous insects. Regards,

Rinaldo Nicoli

Dear, Andrew Paul,  Casper Vanderwoude and Rinaldo Nicoli

Hello ...

Thank you so much your answer, yes...it's reality in my observation, predator remain a wings of their prey.

Regards,

Sri

Birds and bats don't eat butterfly or moth wings either. The low nutrient hypothesis seems like the likely one.

Cheers,  Jim des Lauriers

Dear Sri

In my opinion this issue is related to the digestibility of compound chitin wings. Wings made mainly of chitin is not digestible. The toxic compounds in the affected wing scales. best regards

Dear James Des Lauriers

Thank you Jim for interesting answer.

Regards,

Sri

Dear Prof. Masoud Latifian,

First time I think wing scales avoid predator eat the wings. You true, Troides helena larvae eating Aristolochia leaves contain aristolochic acid that toxic for predators. Also wings contain more chitin that difficult in digestive process in insect stomach. Thanks your  comment here. 

regards,

Sri

I presume this is because the Lepidopteran wings are made up of scales which is mainly a complex of the cuticle, cuticulin, and chitin materials.  some of the scales are also said to be poisonous the reason why you will observe the other body parts are eaten leaving the wings behind. 

Thank you Ruth for interesting answer...