Response of passerine birds and chicks to larvae and pupae of ladybirds

1. Few, if any, experimental tests have demonstrated the anti‐predator protection of the developmental stages of ladybirds (Coleoptera: Coccinellidae) against vertebrates, despite the fact that both the visual appearance of ladybirds and the content of defensive compounds fulfil the definition of an aposematic prey. 2. In this study, avian predators of three species were confronted with fourth‐instar larvae and pupae of the harlequin ladybird (Harmonia axyridis) – a large, conspicuous, and toxic ladybird species. 3. The selected predators differed in their individual experience and attitude to ladybirds. Wild‐caught great tits (Parus major) strongly avoided attacking ladybirds in general, whereas wild‐caught tree sparrows (Passer montanus) were willing to include ladybirds in their diet. Domestic chicks (Gallus gallus domesticus) have never been confronted with ladybirds but usually show avoidance of aposematic signals. In this study, great tits and domestic chicks avoided both developmental stages, but in the case of chicks the avoidance had to be learned over the course of repeated encounters. Sparrow avoidance was significantly lower, with more than one‐third of the prey being attacked and eaten. 4. The protection of both developmental stages of ladybirds is similar to adults, despite substantially different visual appearance.