Rehoming cave spiders at Malham Tarn

Cave spiders at Malham Tarn

We were busy renovating Malham Tarn’s Orchid House when we discovered a colony of cave spiders. As their name suggests, these spiders are more usually found in caves. It is thought that this colony was accidentally brought in by Bradford University archaeologists ten years ago.

The archaeologists were carrying out a survey in a nearby cave and used the Orchid House to store equipment. It is likely that they brought enough spiders in with this equipment to begin a new colony in the disused building.

We have no records of the spiders being in the building before this time and none of our staff remember ever seeing them there before.

What are they like?

Cave spiders measure over three inches across and are among the largest spiders we have in the UK. They are usually harmless but can bite, if provoked, although they are not poisonous.

They have dark bronze bodies and long legs and hate the light, preferring the dark habitat of caves. The spiders are active hunters and eat small insects.

What are we doing with them?

The colony is thought to be about 150-200 strong, with lots of egg sacks promising many more baby spiders to come. As we are developing the Orchid House, the spiders need a new home and we are moving them back to nearby caves, where other cave spiders are already known to live.

How are we moving them?

We are used to trying to do things on a shoe-string and this is no exception. Using a vacuum cleaner on a low setting and an old fish-tank, the spiders are safely sucked up and transferred to individual containers. We quickly found out that they will attack each other if put in the same container.

These are then taken to nearby caves and the spiders tipped out and left to explore and set up a new home.

Can visitors see them?

Cave spiders are not something you usually see, so rather than move them and forget all about them, we've made a ‘spider cave’.

There is a small building next to the Orchid House where we've put a small number of the spiders. Although you can't enter the building, there's a window for you to look through and a small light you can switch on to look at the spiders. They prefer the dark though, so the light will turn off after a short time.