Stereo Vision.
Mantises are primarily diurnal (ie out during the day), as their their hunting relies heavily on vision.
This lovely mantis was closer to me, on a stem of a plant see below.
This is a sub-adult flower mantis, and the small wings that you see on her side will grow to cover her whole body, and allow her to fly. She will shed one or two more times to achieve this.
She then hopped away behind a stem of grass, where her eyes continued to track me.
Mantises have stereo vision and they locate their prey by sight. A small area at the front called the fovea has greater visual acuity than the rest of the eye, and can produce the high resolution necessary to examine potential prey. The peripheral ommatidia, (their compound eyes contain up to 10,000 ommatidia), are concerned with perceiving motion. When a Mantis sees a moving object the head is rapidly rotated to bring the object into the visual field of the fovea. Further motions of the prey are then tracked by movements of the mantis's head so as to keep the image centered on the fovea. The eyes are widely spaced and laterally situated, affording a wide binocular field of vision and precise stereoscopic vision at close range. The dark spot on each eye that moves as it rotates its head is a pseudopupil. This occurs because the ommatidia that are viewed "head-on" absorb the incident light, while those to the side reflect it.