Pit-fall traps are ground-level traps used to catch any invertebrates that may crawl over. 

On soft soil a yoghurt or plant pot can be pushed into the ground and left overnight. Anything that falls into the trap will be caught and can be examined the next day. You may wish to put holes in the bottom of the pot so water can drain through and a protective cover over the top, held up by stones, to prevent rain entering. 

Experiment with the best place to put your trap. You could compare what is found in traps placed near vegetation with those placed on open ground. Remember to check your traps daily and remove them after use.