'Why are all these millipedes showing up in my house?' is a question South Australian pest controller Michael Cutting has been hearing a lot in recent months.

Hordes of Portuguese millipedes are on the march across southern Australia, popping up in bathrooms and bedrooms, and furnishing roads and walking tracks with an unwelcome 'crunchy' carpet.

Mr Cutting's Spiderman SE Eco Pest Management has been called out to child care centres, building developments, aged care facilities and private homes as people seek to rid themselves of the pint-sized pests.

"Most people are sick of them and can't get rid of them," Mr Cutting said.

"They are everywhere. Every client I talk to at the moment wants to talk about millipedes.

"We've found them in some pretty strange places. I have seen entire walls covered with them."

Millions of Portuguese millipedes become active in South Australia in autumn and in spring. ( Supplied: CSIRO )

Staying hidden in the soil during hot, dry weather, autumn and spring rains will see the millipedes emerge in huge numbers, to feast on their favourite diet — leaf litter, fungi and decaying wood.

The name millipede means 'a thousand feet', but the distinctive invertebrates can grow up to 350 pairs of legs during their two-year life span, hatching with just three pairs of legs.

Native to Europe, the Portuguese millipede first showed up in South Australia in 1953 in the town of Port Lincoln and, lacking natural predators, are now widespread across southern Australia.

In the 1970s, residents around the Adelaide Hills area were reportedly removing the millipedes by the bucket-load as the critters multiplied to plague proportions.

Most active at night, the creatures are attracted to light, which explains why they can often be spotted in large numbers on light-coloured walls.

Anyone who has ever been in the vicinity of more than a few squashed millipedes will remember the distinctive smell — a pungent odour designed to repel predators.

"It's not just one that shows up — it's a lot," Mr Cutting said.

Mr Cutting said most people tended to find the millipedes "unsightly and annoying" due to their numbers.

"It is more the inconvenience of them — they are so messy," he said.

"People are having to constantly sweep them up and accidentally crunching them underfoot."

Thousands of millipedes across a popular Mount Gambier walking trail. ( ABC South East SA: Kate Hill )

Strength in numbers

Despite their inferior size, the creatures are capable of incredible en masse feats.

A millipede plague in Perth shot to international fame when it was blamed for a train crash in 2013, after large numbers congregating on the tracks were crushed by trains, making the line slippery.

In America, researchers have even discovered a bioluminescent species of millipede, which emits a gentle blue-green glow at night.

For those who find themselves inundated with millipedes, don't despair.

Mr Cutting said chemical and physical barriers would put a stop to your millipede problem relatively easily.

Although his company uses a people- and pet-friendly spray, stopping up all the little external cracks and crevices will put a halt to their movement inside your house just as simply.

Getting rid of leaf litter will also remove their food source.

He advised using a broom rather than your foot to remove the millipedes, as accidentally crushing them will bring forth that unfortunate lingering smell.

But for the most part, they are a fact of life if you call southern Australia home.