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DickybirdSeptember 1st, 2021, 7:41 pm
Posts: 7The large swimmer mayflies (Isonychia, Siphlonurus, Ameletus) are all described as having tails with numerous hairs all lying in the tail plane, and with those on the outside tails pointing only inward, said to form a propelling fin. Photographs show these hairy tails clearly.

The small swimmers (Baetidae) are often described as having a similar tail arrangement, whether with 3 tails or 2. A number of authoritative drawings (Leonard & Leonard: Pseudocloeon anoka, Baetis hiemalis; McCafferty: Callibaetis, Pseudocloeon) show this pattern. However, as I look through the Troutnut and other pictures, aside from one individual Baetis tricaudatus, which has a few stiff hairs on the middle tail, I can't see the hairs. Are they just too fine for even the high resolution pictures? Am I not looking at the right genera? Do they fall off in captivity? Or, the functionally interesting possibility, that in such small insects the abdomen itself provides all the surface area needed?

TaxonSeptember 2nd, 2021, 5:38 am
Site Editor
Royse City, TX

Posts: 1350
Hi Rich-

My knee-jerk reaction to your question concerning tail hairs would be that, unless a mayfly nymph is photographed while fully submerged, all of its appendages (including tail hairs) tend to be stuck to its body, and as a result, not be visible.
Best regards,
Roger Rohrbeck
DickybirdSeptember 2nd, 2021, 11:59 am
Posts: 7Hi Roger,

Thanks. I hadn't thought of that. But the pictures I was talking about were all Troutnut or BugGuide, and everything else looked really good.

MillcreekSeptember 2nd, 2021, 1:22 pm
Healdsburg, CA

Posts: 356

In photography you are generally trying to focus on as much of the nymph as possible. Generally you are talking about a 5-8 mm organism, with the tails being about a third that length, the side hairs being miniscule, and in most Baetidae being a light or translucent color so it's unlikely you will get much detail. Plus since the tail is on a different plane than the antennae, head and abdomen it will often be out of focus. You can get the hairs in focus but will lose detail on other body parts. About the only way you could get those details in Baetidae would be through microphotography.

You can get some views of the tail hairs by googling Baetis and looking through pictures of nymphs.

And no, the nymphs generally do not lose their small tail hairs by being captured as a look under a microscope would tell you.
DickybirdSeptember 3rd, 2021, 12:52 pm
Posts: 7Hi Mark,

Thanks. Good detail. I take all your points. I was sort of joking about losing the hairs on capture.

I worked harder on Google and stumbled on this
in which Figure 67 might show the answer to my question. Figure 62 on the same plate shows the nymph with apparently smooth tails, while 67 is an extreme enlargment of a section of one lateral tail that shows a dense line of hairs originating along a line on the central margin, all pointing apically and held tightly along the tail shaft.

Although the caption is unhelpful and I wasn't able to open the paper itself, it is inviting to believe that these hairs, which would be relatively pointless as shown, might be deployable away from the tail shaft and form the fan that appears on so many drawings and so clearly on some photos.

Do you (or anyone else reading this) have any definite information on this point? For me, all this is in aid of a statement I would like to make in a document I am preparing that says something like "All (some?, few?) Baetidae, like the large minnow mayflies, have and array of hairs ...."

Best, Rich

Ps. Mark, I'm glad to have heard from you personally. I have been taken by your photos, previously especially of Isonychia, and this gives me an opportunity to thank you for making your work available.
MillcreekSeptember 3rd, 2021, 4:09 pm
Healdsburg, CA

Posts: 356

I think I would just say "Some Baetidae,"

I found some photos of the side hairs in members of Baetidae. They're Israeli nymphs but should give a general idea of the hairs. Here are a couple of links.
KonchuSeptember 7th, 2021, 6:38 pm
Site Editor

Posts: 505
Most--if not all--baetids that come to my mind have lateral hairs on the tails; some have more than others, though, and some don't have these hairs for the entire length of the tails, especially out towards the tip. It's one of the features we use for identification of some of those groups.

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