Think your house is fairly clean? Think again.

Scientists, who are for the first time starting to look at the ecology of the great indoors, have found the average house could have about 100 species of insects, spiders and other bugs living inside.

Among the most common are booklice, dog-food-eating carpet beetles, gall midges and dark-winged fungus gnats.

The "indoor biome" has never really been studied by entomologists. But now they are starting to turn their magnifying glasses to our homes – and revealing an extraordinary array of bugs.

"We know indoor biodiversity is very broad," says Dr Bryan Lessard, an entomologist with the CSIRO's Australian National Insect Collection.

"But no one has really studied this, so it's a research area that's really exciting. There is not much known, and we take it for granted."

Working with a team of researchers from the US, Dr Lessard has been studying the biodiversity of houses in Canberra and on Magnetic Island.

In March they crawled through the homes, peeking under beds and vacuuming carpets in an effort to collect all the insects that call a house a home.

They are still compiling their findings, but a pilot study by the same team in North Carolina last year shows what we might expect.

There, they found up to 211 different types of arthropod – insects and spiders – all coexisting within a single house, with the average house being home to 93 separate species.

The research also found a strong link between a neighbourhood's wealth and a household's biodiversity – probably because wealthier houses tend to have more indoor plants, which encourage bugs inside.

It all lends scientific weight to the old saying: you're never more than three feet away from a spider.

"That's true," laughs David Bock, an environmental scientist with the Australian Museum.

"But most of them are the size of pinheads."

Spring and summer are peak bug season, as the warmth kickstarts their breeding processes, Mr Bock says.

Following a spike in bug numbers, spiders tend to arrive en masse to feed on them.

"In spring, everything blossoms out. But this year Melbourne and Sydney have had slightly wetter, colder winters," Mr Bock said.

"So I don't think you're going to see huge numbers of insects just yet."

Many of the most common household species are remarkably well-adapted to indoor life, and tend to coexist with humans all over the world, says Melbourne Museum entomologist Dr Ken Walker.

In many cases they do well because they like to eat the same food we like to eat.

Booklice are often found merrily munching away in containers of cereal or flour, for example. While disgusting, they are not harmful, Mr Walker says.

"What I often recommend is you just freeze the container that they got into. That'll kill them – and you just add a bit of protein to your flour."

What's in your house?

Photo: Public Health Image Library/Dr Gary Alpert

European house centipede (Scutigera coleoptrata) An introduced species from Spain. Australia has its own native centipedes, but Scutigera coleoptera are more common indoors. Likes bathrooms. Can grow up to six centimetres, gaining more legs as it does. Eats other small insects.

Photo: Stanislav Krejčík / BioLib.cz

Booklice (Psocoptera) Among the most ubiquitous indoor insects. You often find them in flour and rice, but they don't eat the grains – they feed off mould that has grown on the grain itself.

Carpet beetle (Anthrenus verbasci) This species likes munching on carpet fibres, dog food, spider webs – anything, really. "If you've seen a patch of carpet missing they might be the culprit," says Dr Lessard.

Photo: Kugamazog / Wikipedia

Wolf spider (Lycosidae) These common spiders do not make webs but wander through houses to find their prey. Their bites are generally not dangerous to humans. They are known as "vagrant hunters".

Photo: Peter Halasz

Black house spider (Badumna insignis) This critter builds untidy, funnel-like webs near windows and lights to catch flying insects attracted to the light. They are timid, and unlikely to bite. They are generally not dangerous to humans.