BIRDS BUGS & BONES

269 Jun 24 2018 via/src

I've been meaning to message you since the moth appreciation post because like I need to talk/know more about that moth that lays eggs in water? What the f-ing what? That is mental. I didn't know we had aquatic moths! (I currently have lots of Garden Tiger babies at home for a uni experiment. I love my fuzzy babies.)

herchancellor:

nanonaturalist:
Hello, Friend! Isn’t that ridiculous?? I only recently learned about Petrophila moths [link], too, and when I read that about their caterpillars, my mind practically exploded. Nature is so weird. But these moths with aquatic caterpillars caught my notice for a totally different reason initially: they are jumping spider mimics.
You can see from these photos that they’re not very large. If you weren’t really paying attention, you may not even notice anything unusual about them. The first time I saw them, I definitely didn’t notice that they were spider mimics. But one night, I went to a talk about moths, and the presenter talked about these and I thought it was awesome! She had a mercury vapor lamp set up outside after the talk for us to see some moths, and a Petrophila showed up. I was super excited! When I went to add the photo to iNaturalist, thinking I’d seen something new, it turned out I had already seen them at least four times.
You may not even be able to see how these are spider mimics. They don’t really *look* like spiders, do they? But remember, our eyes are much different than insect eyes, and we have the benefit of seeing things from far away. We can see this isn’t a spider. But imagine you are a small predatory insect or a spider, and you are in front of this moth looking at it. What will you see?
Jumping spiders above are Dimorphic Jumper (left) and Bold Jumper <3 (right)
Anyway, back to the aquatic caterpillars. I’m sure you know that most moths and butterflies have perfectly normal caterpillars who eat leaves, make poops, and turn into perfectly normal moths and butterflies. So finding out that one type refuse to play by those rules just seems super weird. But is it, really? Or is it just weird because… well, we have an idea of what caterpillars are supposed to be, whether or not that idea is accurate?
For example, look at some other insect orders with complete metamorphosis (they have larvae, pupate, and then become adults). Flies are a huge group. Where do fly larvae live? You know about maggots and food, but what about mosquitos? Those are flies too, and their larvae are aquatic. What about parasitic botflies that grow in animal tissue? What about gall midges who parasitize plants? Caterpillars will grow up in equally diverse habitats (although, I don’t know of an animal parasite… yet). Same with beetles–larvae will live on plants, underground, in water, in wood…
But let’s look a little closer to moths and butterflies, since most caterpillars are fairly predictable in terms of habitat, and the exceptions aren’t very well known. Here’s a phylogenetic tree showing the evolutionary history of insects. In this tree, branches that are closer together are more closely related.
Note: I found this tree in an image search, but I was unable to locate the original source. I would love to credit it if I can! Let me know if you have seen this in a book before.
In this tree, I have circled the branch including Lepidoptera (moths and butterflies). Look at who else is in that circle: Trichoptera (caddisflies). Below are a couple examples of caddisflies. Chances are you have seen them before (they are pretty ubiquitous near ponds, lakes, streams, and rivers!), but had no idea what they were.
Caddisflies are also very difficult to identify. The one on the left is in the Macrostemum genus (zebra caddisflies), but the one on the right… uh… I’ll get back to you on that one.
There are a lot of moths that look pretty similar to caddisflies, so it’s easy to see that they are closely related.
Left to right: Yellow-headed Lichen Moth, Belted Grass-veneer Moth, Bluegrass Webworm Moth
These look so similar, in fact, you may ask how they even grouped them into different orders. This is easy to answer if you know your scientific names AND Greek!
Moths & Butterflies = Lepidoptera (Lepido = scale; ptera = wing)
Caddisflies = Trichoptera (Tricho = hair; ptera = wing)
Since I have an electron microscope at work (the “nano” in my username refers to my background in nanotechnology), I felt obligated to illustrate this. The white bar on each image shows the magnification. “um” refers to “micrometer,” or 1/1,000 of a millimeter. A human hair is typically about 100 um wide. (If you have questions about electron microscopes, let me know! These things are fun!)
Typical Lepidoptera (Moth & Butterfly) Wing
Above: Images of the scales on an American Snout Butterfly wing obtained with Scanning Electron Microscopy. Compare the scales in the middle of the wing to those on the edge of the wing.
Typical Trichoptera (Caddisfly) Wing
Above: Images of the hairs on a caddisfly wing obtained with Scanning Electron Microscopy. Note the similarities in the how the caddisfly hairs and butterfly scales attach to the wings.
Looking at these images, it’s pretty clear that they are different. But you have to look *very closely* to notice this difference, and when you look even closer than that, you start to see similarities again.
Guess where caddisfly larvae grow up! If you don’t already know about caddisfly larvae, oh boy, they’re fun!
It may be hard to tell, but I took this photo with an underwater camera. Caddisfly larvae build little cases by cementing together stones, pine needles, sand, or a variety of other things. You can sometimes identify the larvae based on what materials they use and what shape the cases are in. An interesting aside: if you raise these, you can get them to build their cases out of whatever you want. At least one person got creative, and I’m happy to see that she is still selling caddisfly jewelry over 20 years later!
I don’t mean to turn this post into an advertisement, but her stuff is beautiful and super interesting. She describes her process and some info about the species of caddisfly she raises on this page of her website [link]. Photo credits go to her–I totally stole these images.
Caddisfly larvae are exclusively aquatic. Moths and butterflies are slightly younger than caddisflies, so they have had more time to evolve their own method of development (mostly on land). I believe the Petrophila moths are one of the older moth genera (but definitely not the oldest!), so they could be like Cetaceans (you know, whales and such who had gone *back into the water* after they realized they were cooler than land mammals).
I have not yet had the honor of witnessing a little baby Petrophila scooting along the bottoms of ponds, eating algae and whatnot, so I don’t have my own photos to share, but there are a couple on their bugguide page [link] (just click the link for “caterpillars” to filter out all the adults). They more or less look like a normal caterpillar, except … a little wetter than usual. The females will go completely underwater to lay their eggs (they will carry a little air bubble with them, apparently). And typically moths don’t live too much longer after laying eggs, so who knows if they ever fly again. I’m sure the fish don’t mind finding them!
I hope I satisfied your desperate yearning for aquatic moth secrets! The closer you look, the weirder nature gets. Jeez.
Posted June 22, 2018 (finally!)
All photos are mine except the caddisfly jewelry, phylogenetic tree source TBD. Everything was seen in Texas except the caddisfly larva was in a stream near Crater Lake in Oregon.
Good post OP.
Spider mimic moths mess me up. They, like, printed a lossy jpeg of a spooky spider on their wings, which is the camouflage solution a seven year old would drum up for a make-your-own-butterfly project five minutes before it’s due. But evolution did this for millions of years. Twice.
Also I once pulled a caddisfly larva out of its trash hole and its legs were way longer and spindlier than I expected on a larva, which filled me with existential dread over my understanding of life on this planet. They’re top quality buggos all around.