Setting up a pit trap?

Question

For small amphibians and or small nocturnal insects.

Answer 1

A pit trap made of a bottle may work, but small creatures would typically be able to crawl out of an actual pit in soil.

The trap door for it may be very difficult to get right, as the weight of the creatures you intend on trapping is very slight, and needs to open at the slightest weight difference.

I designed a mousetrap that worked very well out of a bottle and a book. The bottle sits balanced on the book until a mouse enters the bottle for food and just to satisfy its curiosity, it then becomes unbalanced by the weight of the mouse and the bottle stands upright trapping the mouse inside alive and well. This may be a better idea than a pit trap.

Answer 2

The most important feature is a pair of doors at the top which appear to provide support, but are only slightly heavy on the outside of the pivot so that the slightest weight in the center where they meet allows the animal to drop. Having two doors means the animal can not grab the side of the pit beside one door and pull out. Using balance means the weight to trip is much less than any spring. And having two doors means that if the animal climbs up the wall, it has to get out in the middle to open the door, which means it will probably drop back in if it does get a grip.