With larvae identification school over, it's down to the banks of the Monnow for the next lesson. Haven't worn waders for ages. Our quarry, the riverfly larvae, are found nestling amongst the rocks on the riverbed. To count their numbers, I need to master the subtle art of kick sampling. Right, this looks quite a good place to take a sample. There's a good strong current. Yeah, that's ideal. So put the net down, and then literally just displace the stones. So we're going to take a three-minute kick sample, so you need to time me while I'm doing the kicking. Ready? Okay, go. So I just dislodge the stones. So why is it three minutes? It's just to standardise the sampling, so that everybody's doing the same amount of effort. So I wonder if you have a go now. Yeah, sure. Well I did, so... Right.


幼虫鉴别课结束后，我们该到曼诺河上下一堂课了。几百年没穿过高筒胶鞋了，我们的猎物，河蝇幼虫。在河床的石头间筑巢，为了弄清它们的数目，我需要掌握水底取样技巧。这里看起来是个取样的好地方，这里水流比较强。 没错，很理想，把网放下去。拨开石头，我们将做三分钟取样。所以你要帮我计时。 准备好了吗？ 好了，开始吧。我得把石头踢开。那么为什么需要三分钟呢？ 只是为了使取样标准化，保证每个人的方法力度相同。你想试试吗？ 是，当然。