Simulating darkness using dim red light: a cautionary note based on experience with larval Aeshna juncea (L.) (Anisoptera: Aeshnidae)

Reactive distance and capture suc- cess by A. juncea larvae were studied under 3 light regimes: natural light (400 ± 50 lux), dim red light (2-4 lux), and total darkness (IR-light). Reactive distance did not differ significantly between natural and dim red light conditions, while it was significantly shorter in total darkness compared to natural and dim red light. Capture success was significantly higher under natural light conditions compared with dim red light and dark conditions; there was no significant difference in capture success under conditions of dim red light and total darkness. Results showed that simulation of darkness using dim red light may be inappropriate when studying the behaviour of aquatic insects with well developed eyes.