Home Nature & Wildlife Nocturnal sea slugs don’t bother looking fancy

Nocturnal sea slugs don’t bother looking fancy

By AG Staff • 25 June 2025

Diurnal sea slugs warn off potential predators with their bright colours and striking patterns. Image credit: Dr Cedric van den Berg/University of Queensland

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Sea slugs with the brightest colouration and most eye-catching patterns are active during the daytime, when their appearance is at its most striking, recent research from The University of Queensland confirms.

The study, published in the Journal of Animal Ecology and led by Dr Cedric van den Berg, analysed the colouration and pattern morphology of 45 diurnal and nocturnal east coast species.

“[Diurnal] sea slugs use bright, contrasting colour patterns to send messages to potential predators, like: ‘Don’t eat me, I’m poisonous!’” Dr van den Berg said.

All 45 species of sea slugs that we examined in the study. *Image credit: Dr Cedric van den Berg/University of Queensland*

Scientists have long suspected a link between bold visual signals and daytime activity, but there was “surprisingly little evidence” to back this assumption until now, Dr van den Berg said.

“They advertise their underlying defences, such as nasty chemicals or stinging cells, with bold visual signals like brightly coloured spots, thick stripes and enhanced body outlines.”

“These tactics are strongly linked to being active during daytime when there’s enough light for these signals to function,” Dr van den Berg explained.

“Nocturnal sea slugs don’t need to evolve colours and patterns aimed at signalling to potential predators, because predators are unlikely to use vision to hunt at night when senses like touch and smell are more important.”