SPIDERS
The familiar cave spider is the large Meta menardi. The spider needs space to spin the characteristic orb web which is small considering the size of the spider. It is a large, dark brown, troglophilic cave spider that prefers to inhabit dim areas and areas where the light is reflected. It also appears to be slightly deeper in a cave that has two entrances close by, and in winter. Some arthropod troglodytes move towards the threshold of the cave at wetter times of the year – in winter this may change the dynamics of the food web. It also prefers vertical shafts, presumably more prey might fall in. The webs are orientated away from light – at 90 degrees to the light. The web is found in the shadows e.g. in phreatic pockets and scallops – by spinning them here they may trap fungus gnats seeking shade, or maybe the web is harder for prey to spot and avoid. The web is not spun across the passage unless there is nothing else to anchor web to, it is often parallel to the wall. The spider primarily uses its web as a supportive platform rather than using it to actively trap prey (as with most orb-spinning spiders) as the webs are not stickey.   Some of the outlying threads of the web do act as "tripwires" however to alert the spider to the presence of prey on the walls and ceiling. They feed on woodlice, millipedes, slugs, earthworm, flies (Culex pipiens in particular), maybe the smaller Metellina merianae (but there is no evidence of this). It can gorge itself and may store food by trussing it in the web.

Meta menardii with a woodlouse, Porth yr Ogof.

The female lays a clump of eggs that and spins a silk cocoon around them for protection. You may see these hanging from the ceiling.

Metellina merianae (formerly in the genus Meta) is found in the threshold, often at the entrance itself where it spins a larger, finer orb web across the passage to catch creatures flying in and out of the cave. The spider is a similar shape to Meta menardii, but smaller and brown and grey in colour.

Metellina merianae in Porth yr Ogof.

In the cracks by the cave entrance you might see Nesticus cellulanus. It is a smaller, paler spider that builds a fine, criss-cross platform web that is attached to the walls by longer threads that have a sticky 'gum' drop near the base. These probably trap crawling insects and in this way it avoids competing for the same food as M. merianae.

You may also see sheet webs by the entrance containing silk tunnels. These are made by Tegenaria sp. but the spider is usually well hidden in a crevice behind the web.

There a number of 'money spiders' (e.g. Porrhomma sp.) found in caves. P.convexum is common – but there are few records in Wales. In the dark zone of Ogof y Ci you may find Britain’s only troglobitic spider, Porrhomma rosenhaueri. It is a straw coloured blind spider – but it is only 2mm long and probably hiding in a crack so you will have to look carefully to find one. Other 'money spiders' include Lessertia dentichelis and Lepthyphantes pallidus. Porrhomma sp. webs are often in obscure cracks and crevices in the walls of the cave, and the spiders even harder to spot.

Porrhomma rosenhaueri on flowstone.

All spiders are predatory but they themselves may not have many predators in the cave. Bats do not appear to be interested except possibly Natterer's bat (Myostis natterei) in caves during cold weather or when hibernating. Young spiders (spiderlings) have to shed their skeletons five to ten times (moult or ecdysis) to grow, and often the discarded remains are mistaken for dead spiders. The newly emerged spider is slighlty paler for a while.

PSEUDOSCORPIONS are small and abundant arthropods but are difficult to spot as they are only 2-4mm in length. They are aggressive hunters and use their enlarged pedipalps to catch prey. Once it has sucked up the contents of its prey it can survive for weeks even months without another meal.

Pseudoscorpion Roncus lubricus, Otter Hole

MITES are small relatives of spiders. There are a number of mites found living in Welsh caves and some are probably troglobites. Rhagidia spelaea is relatively common (found in Ogof Ffynnon Ddu and Ogof Clogwyn). Some mites are truly microscopic and go unnoticed. They live in a variety of habitats - some freeliving, some parasitic on plants and animals, others preying on e.g. Collembola. Eugamasus magnus and E. loricatus have been found in Porth yr Ogof and Eglwys Faen. There should be some water mites to add to the list of mites found in Welsh caves. In Ogof Ffynnon Ddu Rhagidia sp. that prey on Collembola are widespread but infrequent (like many cave creatures).

Parasitic ticks and mites in caves are associated with bats.

TICKS The most common tick on bats is Ixodes vespertilionis, the female lives on the blood of the bat and is closely associated with caves.

CENTIPEDES (Chilopoda) are normally regarded as soil organisms and there have been few recordings from caves. They are predators feeding on nematodes, mites and other smaller insects.

PAUROPODA are tiny, blind creatures similar in shape to centipedes that are generally found in soil feeding on dead plant matter.  Although there are no records from Welsh caves there are cave records from elsewhere in the country and they might be found in accumulations of detritus in the threshold zone.

SYMPYLA are slightly larger centipede-like white organisms that also live on dead plant matter in soil.  Scutigerella causeyae has been recorded from Ogof y Ci.  Symphylella isabellae has been found in Guzzle Hole, elsewhere in the country it has been found far into the dark zone. 

MILLIPEDES (Diplopoda, meaning 'twin feet', have two legs per segment) are more common with a number of cavernicole species, some of which are blind. Millipedes feed on plant debris including wood and are particularly common in oak woodlands on limestone, living for several years. Cave forms often have a thinner shell and more sensory bristles than those on the surface. The three species most frequently recorded in Welsh caves are:
Spotted snake millipede, Blaniulus guttulatus, which has rows of spots (stink glands).
Eyed Flat-Backed millipede, Nanogona polydesmoides, (formerly Polymicrodon polydesmoides), which occurs in the dark zone and can be considered cavernicolous.
Brachydesmus superus, a small cream/white millipede.

Millipede (probably Brachydesmus superus), Porth yr Ogof.