THE SOIL FAUNA: ANTHROPODS - The Soil - page 90

F IG. 30
Compound eyes and field of vision of the predatory ground beetle Notiophilus biguttatus. (From T. Bauer,
1981.)
Modern techniques have allowed some fascinating studies to be made on the ad-
aptations that may be needed for a predatory way of life. The two-spotted ground
beetle Notiophilus biguttatus is a common diurnal species, about 5mm long, that
hunts by sight. It has huge compound eyes each containing between 900 and 1250
separate facets. Together, these cover a visual arc of 200° with a binocular overlap of
74° within which it can gauge accurately the position and distance of its prey before it
makes an attack ( Fig. 30 ) . It lives largely on springtails but the larger, surface-living
kinds are hard to catch for they can spring several centimetres to safety if not grasped
firmly at the first attempt. The Notiophilus , therefore, first lines up on its prey and
then creeps forward a millimetre or less at a time with mandibles wide open until it is
between 1.1 and 2.3mm away before making its lunge. An unmistakeable sign that it
is ready to make an attack, usually at about 5mm distance, is when it lays its antennae
back at an angle. If the springtail moves towards it before it is ready, it withdraws a
bit and then advances again until it reaches the critical distance.