One night this week, I heard a neighbor setting off fireworks, and so I walked out into the darkness and down the road to peer into the valley to catch a free show. I watched until the mosquitoes wore me down, and then headed home, not using my flashlight, because I hoped to catch a glimpse of the glowworm which Irene and I had discovered a couple of summers back. We’d been amazed to finally see one in reality after knowing them only from a lifetime of hearing that song, and I hoped to duplicate the sight, but even though we’d caught glimpses of it multiple occasions that summer, we didn’t see it again last summer, and haven’t seen it so far this summer.

As I stepped off the road and onto our driveway, flashlight still off, I caught a glimpse something circular to one side, something which I at first interpreted as having to be a metallic object reflecting the lights from my house. But as I studied it, I realized that this was no reflection. Something was actually glowing!

I could make out a bright, ragged circle a foot in diameter, with other further random bits and pieces of glowing material heading off a dozen feet or so into the woods. The night was so dark that I couldn’t make out exactly what was glowing, so I turned on my flashlight. I was surprised to see that all that was present was wood.

Irene had taken a hatchet to a low stump earlier that day to flatten it to the ground, and what I was seeing was that area of newly exposed rotted wood. (That’s a daytime picture of the area above.) The glowing bits that extended off from what remained of the stump were pieces that’s she’d tossed away.

I shut the flashlight, and studied the area further, amazed. I’d never seen such a thing before, and had never even heard of the possibility. I hurried back into the house to get Irene. We stood together over the glow, awed, and then moved on to the other areas of rotted wood she had disturbed that day. Most were dark, but one other also glowed. I don’t know how rare this occurrence is, but I felt quite lucky to have witnessed this.

Some online research revealed that decaying wood can phosphoresce due to the presence of a fungus known as Agaricus melleus. Most of the reports of this phenomenon are quite old, such as in this letter from an 1873 issue of Nature:

One wet evening last autumn some pieces of phosphorescent wood were brought to me, which had formed part of a dead beech-tree that had been cut down during the day. They shone brightly that evening. The next night they were dark until dipped in water, when the light revived but was much fainter than before. On the third night they seemed to have lost the phosphorescence entirely, for water produced no visible effect on them.

But the reference which fascinated me the most was that of Henry David Thoreau’s first exposure to phosphorescent wood, which he encountered during a trip to into the Maine woods in July of 1844. One night, he happened to see “a perfectly regular elliptical ring of light” which was “not reddish or scarlet like a coal, but a white and slumbering light, like the glow worm’s.” He continued on to write:

I saw at once that it must be phosphorescent wood, which I had so often heard of, but never chanced to see. Putting my finger on it, with a little hesitation, I found that it was a piece of dead moose-wood which the Indian had cut off in a slanting direction the evening before. Using my knife, I discovered that the light proceeded from that portion of the sap-wood immediately under the bark, and thus presented a regular ring at the end, which, indeed, appeared raised above the level of the wood, and when I pared off the bark and cut into the sap, it was all aglow along the log. …

I cut out some little triangular chips, and placing them in the hollow of my hand, carried them into the camp, waked my companion, and showed them to him. They lit up the inside of my hand, revealing the lines and wrinkles, and appearing exactly like coals of fire raised to a white heat, and I saw at once how, probably, the Indian jugglers had imposed on their people and on travellers, pretending to hold coals of fire in their mouths. …

I was exceedingly interested by this phenomenon, and already felt paid for my journey. It could hardly have thrilled me more if it had taken the form of letters, or of the human face. …

Long enough I had heard of irrelevant things; now at length I was glad to make acquaintance with the light that dwells in rotten wood. Where is all your knowledge gone to? It evaporates completely, for it has no depth. I kept those little chips and wet them again the next night, but they emitted no light.

We checked the area the next night, and indeed, the light was no more. But thanks to a fungus unexpectedly revealed in the heart of rotted wood, I feel connected to Thoreau in a way I never have before.