A moisture responsive device is described having a moisture responsive element comprising at least a moisture responsive formation of a first material in association with a less moisture responsive formation of a second material, in that the first material has a greater tendency to absorb moisture and to increase in volume as a result than the second material, the two formations being so mechanically arranged together that such swelling tends to cause mechanical deformation of the moisture responsive element and an actuation member optionally of flexibly resilient material in mechanical association with the moisture responsive element so that distortion of the moisture responsive element in the presence of moisture tends to mechanically distort the actuation member and thereby cause the actuation member to change between at least a first functional state and a second functional state. A method of use, especially in irrigation control, is also described.
