Ladybirds reveal 'honest' signals to predators

The brightness of ladybird colours has been found to reveal the extent of their toxicity.

A research team at the University of Exeter studied five species of ladybird beetles and found that they exhibit different levels of toxicity among and within species. The results also showed that species with the most noticeable colours in their natural environment were the most toxic.

PhD student Lina María Arenas at the Centre for Ecology and Conservation at the University of Exeter said: “Our study shows that not only does ladybird colour 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.”

In the study, published in the journal Scientific Reports, the scientists used water fleas – Daphnia pulex – to test the level of toxicity of different ladybird species. By counting the number of dead fleas in water containing the different ladybird toxins the team established that the five common ladybird species each have different levels of toxic defence. The inconspicuous ladybirds – species with red spots on black forewings – that lack bright colouration were found to also lack toxins.

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

Also, the team measured ladybird predation rates in the field by using artificial models of each ladybird species. They discovered that the bright coloured – red, orange and yellow – models were similar in their survival and were not attacked as much as the brown – representing larch ladybirds – and black models.

“Relatively inconspicuous species, such as the larch ladybird, have low levels of defence and place more emphasis on avoiding being seen, whereas, more conspicuous and colourful species, such as the 2-spot ladybird, openly flaunt their strong defences to predators like birds,” Dr Stevens said.

Paper: http://www.nature.com/srep/2015/150605/srep11021/full/srep11021.html