Drought or leatherjacket damage? How to tell?

Someone asked me recently why their lawn had developed brown patches.

After resisting the temptation to bang my head against a wall and scream "it's the WEATHER, stupid! EVERYONE'S lawn looks like this at the moment!!" I paused and wondered whether it could be leatherjacket damage.

The grass weeds and moss were healthy, which made me suspect it was just scorched. But it there a way of telling without digging a bit up and looking for grubs? The brown patches caused by leatherjackets and drought look very similar to me.

 

The grubs themselves are very hard to find by digging. Try pulling the grass and if it comes away very easily it could be a sign that something is munching on the roots.
You could try watering the effected area in the evening, cover the area with a sheet of polythene (bin bag maybe) weigh down the corners of the polythene. Check the underside of the polythene in the morning to see if there's any grubs stuck to the underside of it. If there is then there's your problem.