How do I catch butterflies for the Professor?

I received a mission from the Professor to help him catch 20 butterflies and he gave me a net to do it with but I can't seem to get it to work! I've tried dragging the net to where the butterflies are, but nothing happens. What do I do?

Butterflies will fly at two different speeds. Watch them a while and you'll notice it. To catch them, equip the net like you did the metal detector and the magnifying glass, get close enough to the butterfly and click on it. Your entity will swing the net and a blue square with a tally will appear.

I've had the problem where I can't get the professor to accept the 20 butterflies now.

Thanks for the advice! I was able to catch the butterflies and give them to the professor. At first, I had trouble getting the professor to take the butterflies, but then I went and caught another butterfly (so then I had 21/20 butterflies) and then right after catching the extra butterfly, without doing anything else in between w/the butterfly net still equipped, I went back to the professor and he took them.