Ciids of change

Time for another tiny invertebrate today - not on a carrot, or among fragments of dead wood, but in an old Ganoderma bracket fungus attached to an old stump waiting to be cut up in our wood store. It clearly had small holes bored into it and there are many fungus-feeding invertebrates, so I had to investigate what lay within - the first thing that popped out was this small (approx. 2mm long) beetle larva...

Small (2mm long) beetle larva found in a Ganoderma bracket fungus

Initially I wasn't too sure what this was - a beetle certainly, but which family? It's almost certainly a 1st instar larva going by the lack of sceloritisation (darkening and hardening of chitin) which makes identification harder as many potentially useful features may be poorly developed. Superficially it looks similar to the Cleridae, but the hairs here are longer and sparser, and the tail 'horns' (cerci) in clerids are incurved rather than upturned. They are also found in carcasses or under bark rather than in fungi. However, although I was certain it was not a clerid, I did start my search among families that are systematically/taxonomically close to the Cleridae.

Fortunately, my first choice turned out to be the right one - the Ciidae, a family of tiny (1-4 mm long) beetles associated with fungi, especially old, decaying brackets and other wood-encrusting forms. They feed on the fungi and several species can sometimes be found in a single fruiting body. As well as being small, the adults are all black or brown, and morphologically very similar - as such they are generally considered to be a 'difficult' group to identify. This is true up to a point as relatively high magnification is needed, x60-x80 or more according to Cooter & Barclay (2006), and there is no easily/cheaply available up-to-date key to the British species - the best is currently Lohse (1967), though there is, I believe, a key currently being worked on. The pair of upturned cerci is typical, and even mature larvae are only weakly sclerotised (there would be more around the head and cerci).

As for which species it is, that's a bit of a guess - I'm not certain the larvae of all species have even been described, but Cis nitidus is a common and widespread species associated with old Ganoderma brackets, so is a likely candidate. Also, given the lack of information on ciid larvae, this is a good opportunity to look at some key features:

Ventral view of the head of the ciid larva - the small brown mandibles are visible, and an antenna (the other appears broken) is indicated by the arrow. It is unclear whether the larva is blind - there are faint indications of what might be ocelli (simple light receptors) but this remains uncertain.

Leg of the ciid larva - the middle left one is indicated by an arrow and bears a pair of tiny claws at the tip (the best focus I could get in the photo, but clearer under the microscope)

The posterior of the ciid larva with a pair of brown, upcurved cerci - also note the bristles which presumably have sensory and/or anti-predator functions.

Beyond this, I would need to raise larvae to adults for identification. If searching for Ciidae, it is important to only take small samples, e.g. from the edge of a fungal fruiting body, as searching is essentially destructive. In this case the bracket is on firewood and therefore has been removed and placed in a container to see what emerges - certainly better than burning it, and if anything interesting appears, it'll undoubtedly be posted here.

Lastly, if you do intend to investigate the Ciidae, it's worth remembering that entomologists have argued over the correct name for this family - Ciidae is now widely used, but you might find it called Cisidae, Cissidae or Cioidae...


References

Cooter, J. & Barclay, M.V.L. (eds.) (2006). A Coleopterist's Handbook (4th ed.). AES, Orpington.
Lohse, G.A. (1967). Familie: Cisidae. In: Freude, H., Harde, K.W. & Lohse, G.A. Die Kafer Mitteleuropas 7, pp. 280-295. Goecke & Evers, Krefeld. [In German]