Saturday, August 31, 2013

Of moths and mites

A Clover Hayworm moth, Hypsopygia costalis, graces my front wall, near the porch light. Beautiful as this moth is, with its maroon wings trimmed in lemon-yellow, it is a rather "weedy" species, as its caterpillars are generalist feeders on a variety of dried plant material, including clover. As I live next to the Ohio State University's farm, there is no shortage of such fare around here, and these beautiful little moths are regular visitors to my lights. I made this image on August 21st.

So, today I was analyzing the image in greater detail with our graphics genius at work, Chad Crouch, to see if it might be suitable for use in one of our publications. With his sharp eye for symmetry, Chad quickly noticed something that I had missed. Click the photo to enlarge, and check the outer portion of the right wing. Mites! Two of them!

Here's a tight crop on that part of the wing, and I've enhanced the mites' color a bit to make them more visible. Well, that was the coolest thing that I had seen all day (yes, I know...), and of course I wanted to know more. Mites are abundant parasites on a huge range of animals, but in spite of the scores of moth photos that I've taken over the years, I had never notice them on moths before.

A bit of research quickly revealed that mites are indeed known as parasites on moths, and the BugGuide website even has a photo of mites - same species presumably - on a Clover Hayworm moth. Presumably the mites in that photo, and mine, are tapping into a wing vein and actively feeding, rather than just hitching a ride.

I found a beautifully written 1967 paper entitled "Mites from Noctuid Moths" that was written by Asher E. Treat and published in the Journal of the Lepidopterists' Society. It appears to be one of the more comprehensive papers on this obscure subject, although as Treat notes, "Here is a garden of wonders for the inquiring lepidopterist, a garden that is virtually unexplored". Although he wrote that 46 years ago, it seems that not many lepidopterists have taken up the quest to ferret out the mystery of moth-borne mites in the intervening years.

Although Treat's work was confined to moths in the family Noctuidae - the Clover Hayworm is in the Pyralidae - much of what he says probably applies to many moth families, and he brings out the commonness with which mites use moth hosts. There is a large group of mites that only infest the ears (EARS!) of moths! These parasites lay in wait on flowers, and when a suitable moth lands and extends its proboscis to tap nectar, the mites quickly scramble up this "gang-plank". Once on the moth, the mites, apparently following a pheromone trail left by the leader, invade one ear, and only one ear, of the host moth. To infest both ears would be a tactical mistake, as the mite colonies apparently result in the loss of the moth's sensory abilities. If mites infested BOTH ears, the moth would not be nearly as capable at detecting bat echolocations and other threats, and thus the moth would be at greater risk of predation. And then the mites' chances of survival and success would plummet.

Now that I am aware that such a Lilliputian world of mites on moths exists, I will keep a much sharper eye for them when photographing living specimens in the field, and perhaps obtain some sharper images. Although, as good as my Canon 100 mm L macro lens is, this is really the job of the bizarre Canon MP-E 65 mm macro lens, and these mites are yet another justification for getting this piece of equipment.

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