On hornet silk as a photodetector: Considerations of current, voltage and resistance

Electric measurements carried out on the silk caps formed by hornet larvae prior to their pupation have shown that under optimal conditions (30°C and 90% relative humidity) there were significant, albeit reversible, differences between the silk response to visible light vs. darkness. Thus, following electrical charging under illumination, we obtained current value of a few nA only, a voltage ranging from dozens to hundreds of mV and a resistance ranging from hundreds of kΩ to several GΩ, Contrarywise, in darkness, the equivalent values were dozens to hundreds of nA, a voltage of dozens of mV and a resistance ranging from several dozens to several hundred kQ. Insofar as these values were concerned, the transition was almost immediate upon a change in the illumination intensity of about 15,000 Lux/cm2. On the basis of these measurable values, the amount of electric charge could be computed in Coulombs, whereupon the efficiency was found to be greater by 1 × 103 -1 × 105 in the dark than in light. The biological rationale underlying these properties and the sharp transition in response to light and darkness are discussed.