It's not a mouse. Nor is it a rat, despite the panicked suggestions of some people who encountered one recently. In fact, it is likely to be a foe of both those introduced and disease-spreading vermin.

It's an antechinus, once known as the 'marsupial mouse', but more accurately placed within the family of dasyurids - which makes it a relative of bandicoots, quolls and even the Tasmanian devil. And like the devil, it's a ferocious predator - and an equally ferocious sexual marauder.

If you see one - and if you live in an area where they exist, you're likely to be able to watch them, as they are seemingly fearless and remarkably curious - you might notice if differs from introduced rodents in the utterly charming way it moves. Instead of scurrying, it gets about in a series of animated, frantic hops, constantly checking for food. Antechinus seem impervious to the laws of gravity, and will climb buildings, hang upside down and stick to almost any surface, it appears.

It's relatively easy to tell the males apart from the females, in the most primal of ways. The boys have a prodigiously large set of testicles, which are quite visible.

As we move toward winter, the antechinus in the region are actively seeking food in readiness for the mating season. They need a lot of food because the mating season is... very, very - very - vigorous.

Their main prey are insects and spiders. Antechinus are predators, which is thankful as they tend to avoid the poisonous baits laid for mice and rats. They will quite happily crunch through the largest of spiders, taking them head and fangs on. They are also known to eat vertebrates when food is short, which means if they discover a nest of baby mice, they won't resist having a feast.

So let's get onto their sex life, because antechinus are one of the more fascinating of marsupials when it comes to sex. That means: they like a lot of it, for long periods, with multiple partners, and they like it rough.

Which is anthropomorphising, of course. It's simply about reproduction, and recent studies have discovered female antechinus thrive on promiscuity. Taking on loads of different sperm results in the fittest being chosen during ovulation - and healthier offspring.

For the males, this isn't the free-love nirvana it sounds. In their hormone-induced frenzy to mate, their bodies release corticosteroids to enable them to keep it up for 12 to 14 hours at a time. This ravages their immune system, their hair falls out and they develop horrendous internal bleeding and tumours. A short time after the season finishes, so does their life.

All male antechinus die following the mating season. The females? They go into a blissful, uninterrupted, sex-free, gestational torpor, to begin another generation.