The anterior lateral (AL) eyes of the orb weaving spiders, Argiope amoena and A. bruennichii, have a single type of receptor cell with a maximum sensitivity at about 520–540 nm. Efferent optic nerve signals control the photoreceptor response in the AL eyes. Specifically, efferent signals decrease the threshold for light responses and change the waveform of responses. Similar changes in the threshold and waveform could be produced by exogenous application of octopamine, suggesting that it is an efferent neurotransmitter.