It's not a sign of radioactivity, but many species of scorpion — including those you're likely to stumble upon in your backyard — do glow a brilliant aqua under ultraviolet light.

In fact, all Australian scorpions have the ability to light up, as do most scorpion species across the world, according to the collection manager for arachnids at the Queensland Museum, Owen Seeman.

"If you take an ultraviolet light out at night … it glows this fantastic colour [that] you can imagine at night really jumps out at you," he told ABC Brisbane's Craig Zonca.

But why? Well, scientists are not quite sure.

"We don't really know exactly why they do it — it could just be an accident, a freak of nature, that all scorpions fluoresce," Dr Seeman said.

"There are other things that fluoresce. There are a few kinds of fish that fluoresce.

"Minerals fluoresce, and clearly they don't need a purpose for fluorescing — they're rocks."

Dr Seeman said when a scorpion was under UV light, chemicals in its outer shell absorbed and then re-emitted the light at a lower wavelength, "so that it shines this soft blue-green colour".

The easiest way to spot scorpions is at night using a UV torch. ( Supplied: Queensland Museum )

He said one theory was that they used the glow to see at night, as their eyes were sensitive to this blue-green colour — but added that there was little UV light at night.

"They're not walking around at night glowing like radioactive scorpions," he said.

Most scorpions in Australia 'are pretty wussy'

Even though the reason for their glow remains a mystery, it can make things easier for scientists out in the field, as the easiest way to spot scorpions is at night, using a UV torch.

And it's not only scientists that might want to get close to these creatures, Dr Seeman said. Despite their reputation, most species in Australia are quite mild.

The desert scorpion, Australia's biggest at around 10 centimetres, is "really big and scary-looking" but has a short-lived sting, he said.

Despite their appearance, many of Australia's scorpions are "pretty wussy". ( Flickr: Ash Meadows/USFWS )

In Brisbane, you can find blue-black scorpions that are extremely placid. Some are even kept as pets.

"But there's also another little mottled scorpion, very tiny, and that one packs a punch," Dr Seeman said.

"It belongs to the group of scorpions that contain most of the highly venomous species in the world, so if you get stung by one of them it hurts more than any other kind of scorpion, despite being our smallest scorpions.

"With Australia's animals, we tend to have the most venomous of many groups, but when it comes to scorpions, most of them are pretty wussy. Scorpions overseas are far more dangerous than those in Australia.

"It's probably because the family of scorpions are very diverse overseas and with only 43 scorpions by chance we only have a handful of small ones."