Have you ever seen a fly catch a spider?

[update] – When I wrote this I thought the creature was a robber fly, now I think it’s a spider wasp. Here’s something you don’t see every day, a large fly like creature walking along carrying a sizeable spider underneath it! Now that’s a prey reversal! A bit like seeing a huge rat hauling a dead cat somewhere. The fly was black, about 4cm in length with long legs that allowed it to carry the spider underneath it and still walk easily. The one I saw was on a mission to get somewhere, it walked quickly over the pavement for about 4m and then climbed a wall before I lost it. It had wings but didn’t try to fly, maybe the spider was too heavy for it. The spider was slightly longer than the fly and looked bulkier, all the spiders legs were gone and it was being carried inverted with it’s abdomen towards the front of the fly.