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'Honest' Ladybugs Reveal their Toxicity

Jun 05, 2015 07:53 PM EDT

In summertime, ladybugs, or ladybirds, are perhaps the most friendly-looking insects around, but be careful, because they are also toxic. And new research shows that the brightness of their color reveals the extent of their toxicity to predators.

The study, which is published in the journal Scientific Reports, also found that the more conspicuous and colorful the ladybird species, the less likely it is to be attacked by birds.

"Ladybird beetles are one of the most cherished and charismatic insects, being both beautifully colored and a friend to every gardener. Our study shows that not only does ladybird color reveal how toxic they are to predators, but also that birds understand the signals that the ladybirds are giving. Birds are less likely to attack more conspicuous ladybirds," researcher Lina María Arenas, from the University of Cambridge, said in a statement.

Although red ladybirds with black spots are most familiar, ladybirds come in all sorts of colors and patterns, from yellow and orange to even camouflaged browns. And their bright colors act as a warning signal, telling potential predators to beware of the foul smelling, poisonous chemicals they use for defense.

To figure out just how toxic ladybugs can be, researchers used a biological assay. They counted the number of dead Daphnia - tiny crustaceans - in water containing the different ladybird toxins. The results showed that five common ladybird species each have different levels of toxic defense. And those boasting the most vibrant colors in respect to their environment are the most toxic.

"Our results tell us that the ladybirds present 'honest' signals to predators, because their color reveals how well defended they are," said Dr. Martin Stevens, from the University of Exeter.

"Relatively inconspicuous species, such as the larch ladybird, have low levels of defense and place more emphasis on avoiding being seen, whereas, more conspicuous and colorful species, such as the 2-spot ladybird, openly flaunt their strong defenses to predators like birds," he explained.

The study is the first to comprehensively show that the level of colorfulness and conspicuousness of different species with warning signals reveals how toxic they are, and that in turn more toxic and colorful species are less likely to be attacked in the wild.

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