Cave Life of Devon

Life in the cave - Spiders and millipedes


Meta menardi is a large, dark brown, troglophilic cave spider that is well known to cavers.  They are orb web spinning spiders and spin the characteristic spider web to help catch prey. Meta spiders need space to create these webs, which are not spun across the cave passage like normal orb spiders unless there is nothing else to anchor the web to. The threads of the web of Meta menardi are not sticky and appear to serve as a supportive platform for the spider rather than directly serving to trap prey, instead the radial threads act as a series of trip lines to detect the presence of potential prey on the cave walls and ceiling.  They feed on woodlice, millipedes, slugs, earthworms, flies (Culex pipiens in particular) and possibly smaller Meta menardi (although there is no evidence of this). It can gorge itself and may store food by trussing it in the web.

Meta menardi, Pridhamsleigh Cavern


Meta menardi prefers reflected light and dim zones (not direct light) and appears to live slightly deeper in a cave during the winter. Movements of different species towards or away from the threshold at different times of year may change the dynamics of the spider’s diet. It also appears to prefer vertical shafts, presumably because more prey might fall in. The webs are orientated away from light – at 90 degrees and are to be 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.
The female lays a clump of eggs and spins a silk cocoon around them for protection. You may see these hanging from the ceiling. 

Metellina (formerly in the genus Meta) merianae 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. It is generally found in the shallow threshold zone, whilst Meta menardi is often found deeper in the cave.  The two species are frequently recorded from the same caves. 

In cracks and pockets in the cave threshold you might see Nesticus cellanus – its creates a fine web of criss-cross threads with 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 Metellina merianae.

Nestiscus cellanus, Spider Cave


There a number of 'money spiders' (e.g. Porrhomma sp.) found in caves. P.convexum is common and has been recorded from Bickington Pot (along with Porrhoma pallidum), Haytor Iron Mine and Pen Recca. Porrhomma sp. webs are often in obscure cracks and crevices in the walls of the cave, and the spiders even harder to spot.  Other 'money spiders' include Lessertia dentichelis and Lepthyphantes pallidus.
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 Devon caves, including members of the genera Eugasmus and Rhagidia, Hirstesia sternalis (Baker’s Pit) Cyrtolaelaps mucronatus (Bickington Pot), Belba pulveruleuta,  (Chudleigh Cavern), Ameroseius corbicula (Levaton Cave) , Clayptostoma velutinus (Levaton and Rift caves), Nycteribia biarticulata (Pixies Hole), Euzetes globulus (Rift Cave) and Euzetes seminulum (Rift and Ware caves)
Some mites are truly microscopic and go unnoticed. They live in a variety of habitats - some free-living, some parasitic on plants and animals, others preying on Collembola and other small insects.  Water mites (Hydracarina) are another group that require further study and will no doubt add to the list of mites found in Devon caves.   Several species of water mite are only known from deep in water-filled gravels. 
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.

Centipedes are normally regarded as soil organisms and there have been few recordings from caves, with most of these being in Devon. They are predators feeding on nematodes, mites and other smaller insects.  The most common species that might be encountered is Lithobius dubosqui (Baker’s Pit and Napp’s), a small, rather short-bodied species that might be regarded as a possible cavernicole.  Other species that have been recorded (generally in the threshold) include Lithobius forficatus (West Ogwell Cave) Strigamia crassipes (Great Rock Mine) and Geophilus electricus (Napp’s). 
The Pauropoda are tiny, blind creatures similar in shape to centipedes that are generally found in soil feeding on dead plant matter.  Polypaurus sp. has been recorded in Baker’s Pit. 

The Symphyla are slightly larger centipede-like white organisms that also live on dead plant matter in soil.  Symphylella isabellae can be found in caves, sometimes far into the dark zone. 

Symphyla on surface of pool, Doghole


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.   The two species most frequently recorded in Devon caves are Blaniulus guttulatus and Nanogona polydesmoides (formerly Polymicrodon polydesmoides), both of which occur in the dark zone and can be considered cavernicolous. Other species include Brachydesmus superus (Torr Bridge Cave), Tachypodoiulus niger (Kitley Rift Cave, Reeds Cave and Napps Cave) and Polydesmus sp.

Polydesmid Millipede, Corbridge cavern



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