WARNING: Gross

It looks for all the world like a cute furry animal curled up in a cosy rock crevice.

In fact, it is very much not that.

It's a horror cluster of arachnids and every single strand of "fur" is a leg attached to a spider piggybacking hundreds of other spiders.

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One tourist found out the hard way when he tried to give the quivering mass a gentle stroke and hundreds of eight legged creatures rushed out.

The man was exploring a cave in Sonora, Mexico with a group of others when they came across the curious clump, news.com.au reports.

Keen to capture the moment on video but too scared to use their hands, another traveller uses a stick to try and prod the creature awake.

To their shock, the clump of "fur" comes alive as hundreds of spiders untangle themselves and scuttle out across the cave floor, sending the group running.

Yep. Just a cute furry animal sleeping in a cosy crevice. Photo / YouTube
Yep. Just a cute furry animal sleeping in a cosy crevice. Photo / YouTube

The most skincrawling moment is when one of the tourists uses his finger to break off part of the cluster, which visibly dissipates as the spiders unlock their legs and run in different directions.

The creatures are a type of opilione arachnid called harvestmen or harvesters, more commonly known as daddy long legs.

They entwine their legs en masse to form large hairy clumps that are easily mistaken for a single animal — especially when the cluster jiggles around or moves along a floor or wall.

Mostly active at night, opiliones usually spend the days clustered like this for warmth and humidity. They release a toxic odour to repel predators and scientists believe the cluster enhance the toxins.

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Give it a pat with your bare finger, why not? Photo / YouTube
Give it a pat with your bare finger, why not? Photo / YouTube

A recent study found climate change is making spiders more aggressive as they struggle to adapt to challenging conditions.

It found freak events such as tropical cyclones could be having an evolutionary impact in storm-prone regions, where the most aggressive spiders have the best odds of survival.