Zombies in the Tunnel

I took myself into a tunnel today in search of overwintering mosquitos and spiders that are fond of the dark. No joy with the mozzies, but I did find plenty of interest when it came to the spiders.

That tunnel is about four and a half feet diameter

This tunnel goes under the road and the water spills out onto the crofts below as a small burn which then runs into the sea. Earlier this year it would have been impossible to enter the tunnel due to the force of water racing through it, but now the stream of water is only a few inches deep and less than a foot wide. Easy access. Headtorch on, in I went...

It didn't take me long to find my first spider, a female Metellina merianae guarding her egg sac

Looking around I saw a few more Metellina merianae on the roof of the tunnel, plus a few unguarded egg sacs. I also blundered face first through a large web which I presume belonged to a Metellina, clumsy great lummox that I am. 

Metellina egg sac on the roughcast between concrete pipe sections

But then it all went a bit kind of grizzly and gruesome. No, I didn't slip and fall into the water (you'll be disappointed to hear), I made a series of pretty yucky discoveries, in an exciting kind of way.

Metellina - does my bum look big in this?

This spider has been colonised, immobilised and then killed by a fungal pathogen, which really is as gruesome as it sounds. It would have been immobile but very much alive when the fungus erupted through the tissue, bursting outwards from within. I don't know how quickly such victims die once the fungus erupts from them, but I hope it's quickly. The fungus then extends upwards to produce the spikes you can see in the image above. It is from these that the spores are released to colonise any spider sitting below or downwind of the infected individual. Considering I was in a tunnel with a decent amount of breeze flowing through it, I expected the fungus to have infected several more spiders deeper within. I wasn't wrong.

This is another Metellina

There could be anything beneath that mass of fungal fruitbodies

This may actually be a second species of spider-killing fungus, again on Metellina

I didn't collect any of these zombie spiders, but I may end up going back to do just that. It seems there are several fungal pathogens that do this to spiders and I'd like to know which one(s) are in that tunnel. The commonest one is Gibellula leiopus, which has recently changed name and is currently known as Torrubiella arachnophila var leiopus. But that is supposed to infect small spiders, not big things like a Metellina. More online digging brought up Engyodontium rectidentatum as occuring on Meta spiders, which are in the same family as Metellina. There are several other species of Engyodontium that occur on spiders, notably E.aranearum which infects Pholcus phalangioides and seems to be fairly widely reported in Britain. So yeah, I need to go back and pop some fungi under the compound microscope and check the spores. I have no problem collecting fungi from dead wood, but collecting from dead spiders seems just a bit kind of gross. But I think I need to do it anyway. I just so happen to know an extremely competent mycologist named Bruce Ing, he lives up near Ullapool. I may send him some images, see if he'd be interested in checking a few specimens. At least I know the ID would be correct if he does it! 

So there you go, next time you find yourself in a 4ft diameter storm drain running beneath a road keep an eye open for zombie spiders. And regular zombies too, I guess. 

Spot the zombies on the roof yet?