The Fluorescent Back Yard (Shallow Thoughts)

The Fluorescent Back Yard

Some years ago, I bought a long wave 365nm UV flashlight through a group purchase the local geology club made.

I had a few UV flashlights, cheap "scorpion lights" you see at gift shops. But it turns out the cheap lights don't really show the fluorescent colors of most rocks very well; this one was recommended by an expert in the geology club as a low-cost entry to seeing fluorescent rock colors. (They told us you can see even more with more expensive lights — with a warning not to get the 6-Watt UV-Tools light, as its performance is very disappointing -- but I went for the entry-level option.)

I used it a few times, marveled at the cool colors, and then put it away. Recently I dug it out again and went walking around the yard after dark.

I live on a hill of basalt, which doesn't fluoresce. But much of the basalt is covered with caliche, a layer of white calcium carbonate. (That's also the best theory for why the town and canyon are called White Rock even though most of the rocks in it are black.) Caliche can form as groundwater evaporates in an arid climate, leaving its load of minerals behind on the rock. But it can also form as a lake deposit: shortly after the basalt was erupted, about 2.35 million years ago, eruptions dammed the ancestral Rio Grande just south of White Rock, creating a lake geologists call Lake Culebra. It filled what's now White Rock Canyon and points above the current rim (like my yard), as well as the entire Española valley, a total of 400 square miles. I'm not sure which process is responsible for the caliche I see here; probably the groundwater evaporation, not the lake deposits.

Either way, I discovered that caliche fluoresces nicely at 365nm, mostly bright orange. So many of the rocks in the yard have at least a little caliche on them that it's very pretty walking around with the UV light.

I also took along one of my cheaper scorpion lights, for comparison. It makes the caliche fluoresces a little, but much less colorfully. I don't know what wavelength that light is; possibly 395nm?

Sadly, there isn't much variety in my yard; I don't seem to have any rocks that fluoresce in colors other than orange or blue-white. I tried the driveway, which has gravel that was trucked in when the house was built, but found nothing besides some small caliche spots. I don't have much that fluoresces in my indoor rock collection either, except for a couple of pieces of fluorite that glow faintly purple; one of them is pale purple to begin with, the other is white-transparent under white light.

Crickets

I didn't see a lot of other fluorescent rocks. But I did see some other interesting fluorescent objects — like crickets! Who knew crickets were fluorescent? I certainly didn't, but they stand out like beacons under UV light, and there are a lot of them in the yard.

Scorpion

A few days after my cricket discovery, I went back out to try to get a photo of one of these fluorescing crickets, and while looking for a cricket, I found something much more interesting: a scorpion! I knew that we supposedly had scorpions here (the experts at the Nature Center tell me so), but I didn't really believe it and had never seen one here before.

When I posted it on Mastodon, someone said it was a bark scorpion. PEEC's arthropod guide says, in red letters, "The potentially deadly Bark Scorpion is not found in northern New Mexico."

A little web searching seems to indicate that we don't have the Arizona bark scorpion, Centruroides sculpturatus, which has a potentially dangerous sting and is the most venemous scorpion in the US, but we might have the striped bark scorpion, C. vittatus, which has a sting that's painful like a wasp sting and can have other annoying symptoms, but isn't deadly unless you're allergic.

I asked for clarification on PEEC's naturalist mailing list; I didn't get an authoritative reply, but one person had been told that the scorpions in Los Alamos and Taos are the Northern Scorpion (Paruroctonus boreus). They have a sting like a wasp.

So I still don't know for sure what sort of scorpion it was.

Shroom

Back by the bike shed, something yellow caught my eye. It turned out to be a strange mushroom of a type I'd never seen before. I went back the next day to catch it in white light, for comparison.

I wonder if other types of mushrooms fluoresce. Can't tell now: we're still in the middle of a drought and I'm surprised to see even one mushroom.

Other Objects

There are also a lot of small bits that fluoresce in the same color as crickets. I wondered if they might be shells, legs or other parts from long-gone crickets; but they might also be some sort of plant matter, like this larger piece.

Quite a few man-made objects also fluoresce interestingly under the UV light. Under normal light, my shoe is light grey all over, with a light pink rim around the heel.

By the way, for someone interested in looking for scorpions, this scorpion hunting page had lots of useful advice on lights and other equipment.