There are many cave species in this group including some troglobites.

The springtails (in the Collembola group) are an ancient group of arthropods, similar forms have been found as fossils that are around 400 million years old. They are wingless ground dwelling insects that require high humidity. Many species have been found in Welsh caves. They are called springtails due to their ability to leap about with the aid of a trigger or ‘spring’. Soil and underground species appear to have evolved a smaller spring, shorter legs and antennae, a reduction in eyes and loss of pigment. They feed on fungal mycelia, bacteria, decomposing plant and animal material.

Two species of springtail on the surface of a gour pool in Ogof Ffynnon Ddu 1. The smaller one (Arropalites sp.) is 1mm in length and jumps readily.

Springtails are most easily found on the surface of pools, some are so small (1mm) they will look like specks of white dust to begin with, but if you observe them for perhaps a minute one might leap a couple of inches – enough to convince you that it is actually alive. They are so light and small they can move about on top of the surface film of the water. Best places to look are still pools and damp mud banks. Onychiurus schoetti is a springtail that is considered to be a troglobite. It is white and very small and has 2 club shaped antennae at one end. Not all springtails seem to jump, some walk about on the surface as if they are grazing.

Diplurans ('two tails') are primitive eyeless insects with segmented antennae that generally live underground in soil and leaf litter. They resemble white earwigs and live on prey and dead organic matter including springtails and fungi. They are unusual in that they are able to regenerate lost body parts. On some species the tails (cerci) are used as pincers, the one in the photograph has very small tails but long antennae and has a droplet of water on its back.

Diplura on wet flowstone. These can also be seen on the surface of the pools in the high level passage of Ogof Clogwyn.

Many species of fly (Diptera) are found in caves but they are all visitors. They are often found in the same place year after year. Mayflies, stoneflies and caddis flies have nymphs that live in the stream for a few years before becoming an adult fly that may only live for a few days. Their nymphs are probably washed into the cave from outside. Some flies need a resting stage as an adult for part of the summer e.g. Stenophylax permistus - a large buff coloured caddisfly. The adults of another species of caddis fly can be seen lining the wall of the stream near the entrance to Ogof y Ci.

Craneflies visit the threshold in summer, they do not feed as adults. The crane fly Limonia nubeculosa is often found in cave thresholds as a summer visitor – it rests with its speckled brown wings covering its abdomen unlike many crane flies. Outside it is found all year round. There are many in the threshold of Cathedral Cave.

Dungflies e.g. Leria serrata (previously known as Heleomyza) visit the threshold – they arrive in autumn and remain until starvation or fungal attack. Maybe they settle somewhere dry in the dark zone in winter and get caught out as air current reverses in summer with the corresponding rise in humidity and condensation. This dampness is ideal for the fungi to attack them. Adults are found all year round in the cave, but why the reason why is not is not clear.

Dungfly Leria serrata

Fungus gnats (Mycetophilidae) such as Speolepta leptogaster are numerous in caves, some consider it a troglobite.The yellow headed transluscent larva (14mm) live in a web of thin threads (looks a bit like a sheet spiders web), and probably live on bacteria and fungi. The tangled mass of threads is to keep the insect from touching the walls, becoming wet and then falling prey to fungi. They can be seen in the roof of the Great Bedding Cave of Porth yr Ogof, a habitat that completely floods from time to time.

Sciara gnats are similar to fungus gnats but the larva has a black head capsule.

 The winter gnat Trichocera maculipennisis is found deep in caves such as Agen Allwedd and Ogof Ffynnon Ddu along with its yellowish larvae.

The common mosquito (Culex pipiens) - inseminated females overwinter in cave thresholds and then leave the cave in spring for a blood meal, usually from a bird (not from humans). There are several generations a year.

The Tissue moth (Trichosa dubitata) and the Herald moth (Scoliopteryx libatrix) are common in cave entrances such as Eglwys Faen. Both overwinter in the cave (they do move around the cave during this time). The Tissue moth settles closer to the entrance and lower down the wall than the Herald moth. The caterpillar eats buckthorn and blackthorn.
The Herald moth stays underground for up 10 months, it is often found in the dark zone beaded in moisture. It is unlikely the 10 months is all hibernation, part of this time could be to allow the ovaries to develop. It keeps its head pointing away from the light. The caterpillar eats willow and poplar.

Herald moth in Eglwys Faen.

Fleas are common on bats. They are small wingless parasites noted for their ability to leap.

Beetles - many species are cavernicoles. members of the Choleva genus are found in the threshold feeding on detritus and fungi. During summer they create a clay cell and re-emerge in autumn (a summer diapause).

A little orange beetle called Trechoblemus micros has blind larvae and has been found in Otter Hole and Ogof Ffynnon Ddu. The adult has eyes and does not appear to have evolved for a life in the dark – even though it is only found in caves. It is a predator and relatively common in British caves.

The rove beetles have a number of species found in Wales - Quedius mesomelius and Lesteva pubescens have both been found in Porth yr Ogof. This rove beetle was photographed in Eglwys Faen.

Water and diving beetles are found in caves, this photograph is of a diving beetle found in a gour pool at the bottom of the creek in Porth yr Ogof, probably washed in during a flood.