I think this is a juvenile Argiope spider.  With its legs fully spread, it was about the diameter of a quarter, and its web was about the size of my hand.

During a brief stop at our family’s prairie this morning, I noticed a small spider on its web, and set up my tripod to see if I could photograph it.  Just after I got a couple nice photos, a grasshopper nymph blundered into its web, and the spider leapt into action.  I tried to get pictures of it as it was quickly wrapping the little grasshopper, but I only managed one – it was moving quickly, and there was some vegetation in the way.

I managed to get this shot when the spider paused briefly while wrapping the grasshopper nymph. The image is a little fuzzy because I was shooting through some grass leaves, trying not to disturb the action.

However, once it had its prey stabilized, the spider slowed down and I was able to watch and photograph it for the next 10 minutes or so as it waited for the nymph to become sufficiently paralyzed.  When I finally had to leave, the spider hadn’t yet started to feed.  Instead, it was perched above the nymph with two legs resting on the nymph like it was feeling for a pulse.  Every time the nymph twitched, the spider quickly pulled its legs back as if it had touched a hot stove.  Very carefully, I pulled my tripod away and left the spider to its meal.

This was shortly after the spider finished the wrapping process. You can still see the silk attached to its spinnerets (near its rear end).

…waiting for the grasshopper to stop kicking… I assume spider got to eat it eventually, but I had to get to work.