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I reared this adult male P. bairdii (or is it P. machaon bairdii?) that has noticeably larger wings on its right side. The difference isn't huge but clearly evident. Occasionally I'll net wild local Papilio's (P. rutulus, and P. eurymedon in particular) that show the same imbalance although sometimes it's the left side wings that are larger. Any ideas as to what causes this?

Papilio_indra wrote: Thu Jun 19, 2025 6:20 pm I reared this adult male P. bairdii (or is it P. machaon bairdii?) that has noticeably larger wings on its right side.

Papilio bairdii was confirmed as a separate species to P. machaon by Condamine et al. (2023) (see https://forum.insectnet.com/viewtopic.php?t=930)

Papilio_indra wrote: Thu Jun 19, 2025 6:20 pm Occasionally I'll net wild local Papilio's (P. rutulus, and P. eurymedon in particular) that show the same imbalance although sometimes it's the left side wings that are larger. Any ideas as to what causes this?

As for size difference between the two sides of a butterfly, I have seen very occasional papered specimens with this anomaly but don't know what causes it. Do the wild caught specimens fly slightly differently due to the imbalance?

Adam.

Thanks Adam for the clarification on the Latin name.
The wild specimens do tend to fly somewhat more erratically and with seemingly less control.

Just how nature works. Most things are not perfectly symmetric. People, for example, will have arms and legs that are different by a few mm. Some people have differences that are much more pronounced, perhaps 1-2 cm, which will affect the tilt of their pelvis and posture.

This differentiation in wing size is common, and I see it most often in Speyeria.

These lopsided wings occur in different butterfly families as well; the following specimen was a very poor/awkward flier which first drew my attention to it...

Common Wood Nymph - Cercyonis pegala ino
John K.

Impressive specimen John !