Why beautiful bugs seen in Sydney yard could become your 'worst nightmare'

A Sydney resident was at first excited to spot the colourful insects in his backyard.

A swarm of brightly coloured bugs caught the attention of one Sydney resident over the weekend, yet there is much more to this native insect than first meets the eye.

Known as Harlequin bugs, these insects have bright metallic colouration and even stand out against flowers across the east coast of Australia thanks to their distinct shells. However their presence isn't always a welcomed sight in Aussie yards.

"The colour is associated with warning," Australian Museum Entomologist Dr Chris Reid told Yahoo News Australia. "When you handle them they produce a nasty smell ... They're a stink bug, its a pest."

The beautiful harlequin bugs can be seen in a swarm against a tree trunk on the left. On the right a person can be seen holding a Harlequin bug.
The 'beautiful' harlequin bugs are known to give off an unpleasant odour when disturbed. Source: Facebook

The "beautiful" bugs are renowned for the not-so-pleasant odour they produce when disturbed — leaving Aussie gardeners with the decision to either leave the pest on their plants or face an unpleasant smell when attempting to move them.

Harlequin bugs notorious for being 'smelly'

The Sydney resident shared an image of the insects online and admitted he mistook them for "brightly coloured rocks" before taking a closer inspection. However it appears the majority of people online were well-versed with these native insects, with one woman saying they were her "worst nightmare" as a gardener.

Left, a swarm of bugs can be seen on a leaf. Right, a handful of the bugs can be seen on a fence post.
Harlequin bugs are found across the east coast of Australia and mostly eat young plant shoots. Source: Facebook

Despite their stench Harlequin bugs are not harmful to humans, but instead wreak havoc by piercing plant stems and eating sugar-rich liquids that help vegetation grow, with flower buds also dropping prematurely from the bugs' interference.

They are considered a pest to cotton plants, known to introduce a fungus which rots the cotton ball.

The insects grow around two centimetres in length, with their colour indicating their sex. Females are mostly orange with black and males are often blue or red.

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