Pitfall trap

Active collection may be difficult or time-consuming, especially in habitats where it is hard to see the animals such as in thick grass.

A little detergent is usually added to break the surface tension of the liquid to promote quick drowning.

Lures or baits of varying specificity can be used to increase the capture rate of a certain target species or group by placing them in, above or near the trap.

An animal's trappability depends on the structure of its habitat (e.g. density of vegetation, type of substrate).

The capture rate is therefore proportional not only to how abundant a given type of animal is (which is often the factor of interest), but how easily they are trapped.