When you think of slugs, you most likely think of the slimy-looking, brown, black or grey creatures that you see slithering around after a rainstorm.

But this title also applies to some of the most vibrant and diversely colored and patterned creatures on our planet: you just need to know where to look.

That’s because, under the watery cover of our oceans, sea slugs exhibit vivid violets, luminous yellows, vibrant oranges, sharp greens.

But the reason why they are so bright defies the logic that our land-based slugs live by – and this may be the reason for their survival.

Unlike land-based slugs, which camouflage in dull colors to avoid the gaze of their most prevalent overhead predators (birds), sea slugs deliberately stand out in the most vibrant shades possible.

And this is for the same reason: to avoid being eaten.

Though this seems nonsensical, their evolutionary adaptations are actually sound. Just like animals in the jungle (think poison dart frogs for example), the brighter you are, the less desirable you should be to eat. That’s because bold colors signal poison, and something that very definitely shouldn’t be eaten.

After all, nothing that wasn’t poisonous would have the audacity to stand out… right?

However, new research from scientists and marine biologists spread across the UK, US and Australia have sought to understand once and for all exactly how the aposematism (colorful nature of toxic species) works – and how they adapt if sunlight isn’t available to show their true colors.

The results, which have been recently published in the Journal of Animal Ecology, explored the color patterns of 45 different species of sea slug found in the eastern seas around Australia.

Overall, 346 individual sea slugs were observed, to understand how daylight coloration (which allows the sea slugs’ vibrant coloration to be seen) correlated with the activity patterns of the creatures.

And through their data, they discovered that the most sea slugs with the most variation in their patterns were far more likely to be active in daytime, with much brighter colors too.

As the researchers note in their paper, this suggested that they had evolved in line with their daytime activity, with the most brightly and vividly patterned individuals less likely to get preyed on, and thus to reproduce and pass on their ostentatious displays:

“We found that daytime activity in heterobranch sea slugs was associated with a distinct, highly descriptive set of spatiochromatic image statistics. Specifically, diurnal species were more boldly patterned than nocturnal species, exhibiting increased colour, luminance and pattern contrast, indicating the presence of visual signalling and, thus, visual predation as a key driver of heterobranch sea slug phenotype.”

All in all this suggests one thing for sure: boldness isn’t just a fashion statement for these sea slugs, it’s a way of life.

Like quite literally, over generations it is keeping them alive.

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