The fungus gnat larvae of Mycetophilidae 

Apart from the larvae of Forcipomyiinae, the biting midges- , another very commonly seen larvae in leaf litter and on rotting logs are those of a few subfamilies of the Mycetophilidae, a family of fungus gnats. Their latin name literally means mushroom lovers.

The web-spinning Sciophilinae and Keroplatinae larvae are normally found under bark and fallen logs, living in a semi-manufactured environment, surrounding themselves with a webbing or in a sticky, mucilaginous tube that they travel backwards and forward in. They're slime travellers.

They usually eat fungal hyphae, myxomycetes and spores, although some species can be predatory. A noteworthy species is Planarivora insignis, an endoparasite of Tasmanian land planarians.

Certainly in temperate regions, they are also a useful bioindicator of a relatively undisturbed woodland or forest.
Many species of the Keroplatinae subfamily include droplets of oxalic acid amongst their webbing which quickly mobilises and kills small prey, as seen in the photo below.

In Australia and New Zealand, some species in the genus Arachnocampa dangle threads beneath them, loaded with sticky droplets, fishing for small flies. When one is caught, the thread is pulled back up and ingested along with the fly. As an extra attraction, they are also bioluminescent. The Waitomo Caves in NZ are world famous because of this and contain mainly thousands of the larvae at one time, lighting up the cave ceilings and tourists’ faces with an unearthly glow.

Some other species in the same group are also able to glow, including some from the UK, although not to the extent of Arachncampa.

If you pick wild mushrooms, then you will have already come across the larvae from some of the other subfamilies of Mycetophilidae, eating holes and wriggling under the knife or in the frying pan. They are also a common problem in commercial mushroom growing.

Mycetophilids, like the ones here, have specialised mouthparts, enabling them to spin a sticky web in order to control the humidity of their environment as well as providing some safety against predators.

Some other genera in the Mycetophilinae subfamily that also live amongst the rotting wood and fungal hyphae also have some other bizarre adaptations as larvae. This Epicypta species below makes a protective mound or mounds on top of its body, made from its own frass/faecal matter, covered in mucus.

I know.

Another, like this Phronia species below collects frass, debris and its own faecal matter and creates a glorious conical structure, indistinguishable from bark until it shifts and lifts and begins to move….