Come across this one and you could be forgiven for doubting it is a moss at all. Bug moss (the genus Buxbaumia) has almost no leaves and next to no green plant to point at. What catches the eye is a single swollen, lopsided capsule on a short reddish stalk, rising straight out of rotten wood or bare earth, looking far more like a small fungus or a stranded seed than anything you would call mossy.
Free PDF
Get the free Moss Care Cheat Sheet
One printable page on light, water and patience for terrariums, walls and gardens. Leave your email and pick it up, plus occasional unhurried notes on growing moss.
Free, one click to unsubscribe. The download starts as soon as you have signed up.
Almost all fruit, barely any plant
In a normal moss the leafy green cushion is the long-lived part, and the stalked capsule is a passing stage that grows out of it, fruits and withers. Bug moss turns that round completely. Its green body is cut back to a film of fine threads and a few leaves so small and so short-lived that you need a lens and lucky timing to catch them at all. For most of the year the plant is, to the eye, nothing but its spore capsule. Because the green part is so slight, early botanists puzzled over how the thing fed itself; the answer is that the persistent mat of threads, the protonema, does the photosynthesis, very likely with some help from fungi in the soil. If the two-part life of a moss, the green plant and the capsule it carries, is new to you, how a moss is built lays it out.
The lopsided capsule
The capsule is the whole show, and it is a strange object. Set it against the near-absent plant below and it looks enormous, an obliquely egg-shaped pod a few millimetres long, flattened and tilted on its upper face as though someone had pressed a thumb into one side. It ripens from glossy green to a dull reddish-brown and sits on a short, stout stalk that is rough to the touch in some species. That flattened top is not an accident; it helps the capsule flick its spores out into passing air and rain. The odd shape is also where the names come from, bug moss, bug-on-a-stick, and for one species the humpbacked elf, all of them trying to pin down a form that does not look like the rest of the family.
Rotten wood and old woodland
Two species turn up in Britain, and they keep slightly different company. Buxbaumia aphylla grows on bare, disturbed mineral soil, the crumbling edge of a sandy or peaty bank, a track-side, sometimes ground that has been burnt. Buxbaumia viridis wants decaying logs and stumps in damp, shaded, undisturbed woodland, and its presence is taken as a sign of old, little-managed woods, the sort that have carried dead timber on the floor for a very long time. That second species is scarce enough to be protected under European law, so it is never one to pick. Both ask for shade, steady damp and something dead to grow on, which is one more reason to let a fallen log lie rather than tidying it away; the thinking behind leaving deadwood runs through Britain's temperate rainforest.
Why it is so easily missed
Size is most of it. The capsule stands only a centimetre or so high, brown against brown wood and brown soil, and the green plant that might catch your eye in another moss is simply not there to help. It shows itself by season too, the capsules ripening through autumn, winter and early spring and then gone. Most people who find bug moss find it because they went looking, kneeling along old logs with the light low and raking. I will be honest that I have never yet turned one up myself, for all the rotten stumps I have peered at, which puts it on the short list of mosses I would most like to meet.
If you are lucky enough to find one
Treat it gently. Photograph the capsule where it grows, note the wood or soil it sprang from, and take nothing, the more so if it might be the protected B. viridis and you cannot be sure which you have. A record with a good photograph, passed to the people who map these things, is worth far more than a plucked capsule in a tin; recording moss covers how to send one in. Bug moss is never going to carpet a wall or furnish a terrarium. Its whole appeal is the surprise of it, a moss pared back until almost nothing is left but the part that makes the next generation.