A species of British moth uses cyanide-based toxins and bright red spots to warn off predators, new research suggests.
Burnet moths, which are found in many parts of the UK including Cornwall, have a natural variation in their wing markings and scientists wanted to see whether that gave an indication of how toxic an individual moth might be.
While smaller and paler red forewing markings were associated with more cyanide in females, size and brightness of wing colour were no guide to cyanide levels in males.
Scientists at the University of Exeter examined the wings of six-spot burnet moths using a model that can detect ultraviolet light, which is invisible to human eyes but visible to many of the birds that prey on moths.
“Many animals use aposematism (warning colouration) to tell predators it would be better to find lunch elsewhere,” said study author Emmanuelle Briolat, of the University of Exeter.
“Such warning signals are generally ‘honest’ overall – meaning the markings genuinely indicate poison.
“However, it’s less clear whether individuals within species vary in their markings according to how much poison they have.
“In the case of burnet moths, the weak correlations we found suggests the evolutionary pressures are more complex than simply driving colours to match toxicity levels.”
One reason burnet moths may not advertise how poisonous they are individually is that potential predators need no extra warning to leave them alone.
“These moths are highly avoided,” Ms Briolat said.
“There have been reports of burnet moths being eaten by several species of birds, but these instances are rare, and most of the volunteers and researchers we worked with have never seen anything eat one.
“If the moths’ defences are very potent, and predators have a strong incentive to avoid them, there may be little evolutionary pressure for the moths to provide more detailed information on the exact levels of toxins.”
– The study, Sex differences but no evidence of quantitative honesty in the warning signals of six-spot burnet moths, is published in the journal Evolution.