Cave Life of Wales
  
     
 
 

Life in the cave - Spiders and millipedes

 

The familiar cave spiders are members of the Meta genus. They are orb web spinning spiders and spin the characteristic spiders web to catch flying creatures (and anything else). Meta spiders need space to create these webs.

 Meta merianae is is found in the threshold, often at the entrance itself where it spins an orb web to catch creatures flying in and out of the cave. It is a similar shape to M. menardii, but is smaller and brown and grey in colour.

 

Meta merianae in Porth yr Ogof.

 

Meta menardii is a larger, dark brown, troglophilic cave spider that is well known to cavers.

It prefers reflected light and dim zones (not direct light) and appears to be slightly deeper in a cave that has two entrances, 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 they are simply harder for prey to spot.

This spider does spin orb webs – but not across the cave passage like normal orb spiders unless there is nothing else to anchor web to. They feed on woodlice, millipedes, slugs, earthworm, flies (Culex pipiens in particular), maybe the smaller Meta menardi (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 in 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.

Meta menardii spinning silk coccoon in Porth yr Ogof.

 

In the cracks by the cave entrance you might see Nesticus cellanus – its web consist of long threads stretching down to the floor and out to the walls – at the base of these threads are sticky droplets to catch crawling insects – in this way it avoids competing for the same food as M. merianae.

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.

Spiders may not have many predators in the caves - bats do not appear to be interested except possibly Natterer's bat (Myostis natterei) in caves during cold weather or when hibernating.

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.

Parasitic ticks and mites in caves are associated with bats. The most common tick on bats is Ixodes vespertilionis, the female lives on the blood of the bat and is closely associated with caves.

In Ogof Ffynnon Ddu Rhagidia sp. that prey on Collembola are widespread but infrequent (like many cave creatures).

 

Centipedes 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.

Millipedes 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. Porth yr Ogof and Otter Hole have produced a number of species.

Millipede in Porth yr Ogof.
  

 
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