Hey! So the luna moth I recently posted on iNat got me thinking. All the luna moths I've seen (in pictures) are much larger with brighter green, translucent wings. That's why I wasn't sure if it was Actias luna, or just in the genus Actius. I guess the same can be said for the flannel moth I posted, too. It's so close, but a little different. Is this just normal species variation? Or something else? I figured if anyone could answer, it'd be you! Pleasexthanks
Hello (finally)! You are absolutely correct to think this is normal species variation, and this is one of the trickiest parts about learning how to identify any type of living organism. How do you know that a Chihuahua and a St. Bernard are the same species without memorizing all the dog breeds?
There are key morphological features that are still the same within a species, even if they are vastly different sizes, shapes, or colors. Range is also extremely important when you are identifying species. Actias is a fairly small genus, with approximately 25 species worldwide. If for no other reason, your green moth has to be Actias luna because of those 25 species, only one exists in North America.
Naturally, you may wonder why is there so much variation? Well, why is there so much variation between people? Why are some people tall when others are very short? Why do some people have brown eyes, when others have green eyes? The same factors can influence animals in similar ways, even if they are vastly different species.
Genetics: Maybe your moth had the “short” gene!
Sex: Males/females of the insect world sometimes look so different, you wouldn’t believe they were the same species unless you studied them. Size differences are common, especially in species where the females lay hundreds of eggs.
Diet: If you have a caterpillar who is eating a nutrient-poor food, or who has difficulty finding enough to eat, they will mature more slowly, and will be smaller as an adult as a result. Also, some species of animals will be different colors depending on their diet. For example, Flamingos are naturally white!
Above: Two Polyphemus Moths, scaled so the rulers match up. Top is a male who had been exposed to pesticide as a caterpillar, and was smaller than average as an adult. Bottom is his wild (and very healthy) mother.
Health: Related to diet, if a caterpillar survives having parasites, was exposed to pesticides, or had an infection, if they survive, they will likely be smaller as an adult.
Injury: Once the moth emerges from their pupa, they have to deal with birds biting at them, surprise rainstorms, spider webs, and all sorts of other dangers. The color on moths’ wings are the result of scales, and these scales can easily rub off as they avoid dangers (or they can lose parts of their wings!). If you are used to seeing Luna moths with mostly transparent wings, and you see one that is very solidly colored, it’s likely you met him when he was brand-new!
Above: A Snowberry Clearwing moth… before his wings lost their scales to become clear!
I hope this helps, and congratulations on seeing a Luna Moth, I still haven’t met a wild one!
October 22, 2018 (SORRRRRY)