Bugs sunbathe to 'stay healthy'

A western boxelder bug in the sun

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Bugs that sunbathe do so to stay healthy and fight off germs, according to scientists.

Western boxelder bugs are considered 'pests' by some in the US where large groups sheltering from cool weather can enter homes.

The insects are known to release strong-smelling chemical compounds when grouping together in sunlit patches.

Researchers have found that these chemicals help to protect the bugs by killing the germs that live on leaves.

The study was conducted by Joseph J Schwarz and colleagues at Simon Fraser University, Canada and their results are published in the journal Entomologia Experimentalis et Applicata.

A group of western boxelder bugs The bugs can 'swarm' houses in autumn

Named for their favoured habitat of box elder trees, adult bugs grow to an average of 1cm long and can be found in large groups numbering thousands of animals.

When the weather cools in autumn, the insects can move into human homes, surfacing occassionally to soak up the sun before leaving again in spring.

Groups of the insects are also known to emit chemical odours, known as "monoterpenes" from glands at their rear.

In the past scientists have theorised that these compounds could act as a defence or play a role in reproduction; attracting mates and repelling competition.

However, in their study, Mr Schwarz and colleagues found that the chemicals were emitted specifically during sunbathing sessions and did not seem to communicate anything to other bugs.

A Bug's Life

Insects make up a huge proportion of the living organisms on the planet; so you do not have to go far to find them yourself.

Instead, the team discovered that the compounds helped to keep the bugs germ-free.

Bugs in the sunshine were observed "grooming"; wiping their feet and legs across the glands that produce the chemicals.

Under a microscope, researchers found that the chemicals engulfed the fungal microbes that thrive on leaf surfaces, altering their cell structure to prevent them from invading the bugs' bodies.

"We were very surprised," said Mr Schwarz. "The resulting synergism of sunlight and bug-produced chemicals to kill pathogens is simply amazing and heretofore was unknown."

Solar powered

Photosynthesis, harnessing the power of the sun to produce energy, is a common strategy in plants.

A western boxelder bug grooming The bugs wipe chemicals from their rear onto their legs and feet

Some animals, including sea slugs and salamanders, have developed symbiotic relationships with plants in order to use sunlight as an energy source. By accommodating microscopic algae in their own cells the animals can benefit from the plants' energy production.

But, Mr Schwarz suggested, the discovery that western boxelder bugs are able to use the power of the sun without relying on plants places them in an elite group.

"If western boxelder bugs can convert the suns' solar energy to fuel chemical work without the aid of microbial symbionts this would be a spectacular accomplishment in the animal kingdom," he told BBC Nature.

The only other insects known to "harvest light" are Oriental hornets and scientists are still investigating how the wasps use this adaptation.

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