Spider and fly

Identification - unidentified.

I don't normally think of spiders as a hunter of caterpillars, but I have seen a few recently, they are definitely on the menu. What was unusual here, is that this small fly considered the caterpillar as part if its menu too.

The shots of the fly feeding didn't come out well, mainly because I failed to see the significance at the time and was concentrating on the spider. The fly jumped on to the caterpillar for a feed and was ignored by the spider.

I have seen this behavior before, but not noted it. Maybe this is another of those symbiosis things. But again, I don't see what the spider gets out of the arrangement.

Dave