Cellar spider with cluster fly
This spider caught a fly near our kitchen sink (behind some potted plants) on December 27, 2018.
Neither of these is a new species for this site (the spider is a Cellar Spider, Pholcus phalangioides, and the fly looks like a Cluster fly, genus Pollenia). But, I haven’t shown one being eaten by the other before.
We can see what an equalizer webbing is for the spider. The body of the fly is several times larger than the body of the spider, and it is pretty clear that the only reason she was able to handle it at all was the fact that she could quickly truss it up with a sheet of webbing so that it couldn’t get away. She could then inject venom and digestive juices into it at her leisure, without worrying about it fighting back.
So, anyway, the cellar spiders kind of occur anywhere in our house that is near a water source, particularly the bathrooms, kitchen sink, and the laundry room. They mostly stay out of the way, and as you can see they eat a lot of things that would be considerably more annoying, and so we generally leave them to it.
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I often wonder how house spiders find enough to eat. How often to they need to dine to survive?
I don’t think they need to eat all that often, especially not if they get a windfall like this. Hanging around a web waiting for something to blunder into it is not a very high-energy lifestyle. I expect that this fly was probably enough to last this particular spider for a couple of weeks. As long as she has access to a water source to keep from drying out, she should be all set.
I think they also catch a lot of things like fungus gnats (from houseplants), dust mites, springtails, and the like that are too small for us to easily notice, but are big enough to make part of a balanced breakfast for a small spider.