Objects of an unnatural lust

The dungfly is paralysed in a perching position The attraction of dead flies may be hard to imagine

When dungflies and houseflies become infected with a certain fungus, strange behaviour can ensue. Malcolm Smith reports Anyone who has had fleas knows how irritating and embarrassing such a parasite can be. The uninvited visitors may even alter the behaviour of their hapless human host: more frequent scratching; dusting with insecticidal powders; maybe even a reluctance to mix with colleagues and friends.

But these are minor changes in behaviour compared with the transformation some hosts endure when parasites overtake them. When a fungus called Entomophthora grows on and inside its dungfly host, the creature becomes paralysed in a bizarre perching position it never adopts naturally.

The fate of the dungflies, however, is as nothing to the effect the fungus of a related species has on the common housefly. This creature has never had a good press. It feeds on just about anything but has a particular fondness for decaying bits of plants and animals. The problem is that traces of wherever it last ate stick to its feet, carrying disease-causing microbes to its next meal, which might be food meant for human consumption.

Nor has its image been improved by the way it has figured in horror films and science fiction. But those flies infected with the fungus meet a fate beyond even the imaginings of Hollywood film-makers: they end up as the objects of necrophiliac lust by their uninfected fellows.

But first the dungflies, whose fate was recently reported in Proceedings of The Royal Society (B. vol 258: 187-193). Dr David Maitland of Leeds University has been studying their death throes, and suggests the fungal parasite uses the flies to give it a better chance of dispersing its spores, and thus to infect ever more flies. He has coined the apt title "enslaver parasites" to describe their highly peculiar actions.

Dr Maitland studied the flies at two Yorkshire locations. At both, healthy yellow dungflies always perched on the upper surfaces of leaves - nettles and thistles are particularly favoured - low down on the plants. They showed no particular preference forthe wind direction they faced, tending in most cases to perch facing outwards on their chosen leaves.

No less than 91 per cent of parasitised dungflies, before they were killed by the fungus, clung to the underside of leaves towards the top of the plant. So they were invariably above the healthy dungflies. What's more, most faced into the centre of the plant, adopting a highly artificial, head-down, abdomen-up position and favouring the plant's down-wind side.

So why the big difference? Dr Maitland reckons that healthy flies perch the way they do because of the need to be vigilant. Such vigilance is required if they are to maintain or defend their own little territory, find mates or avoid predators. Parasitised dungflies clearly are not being vigilant. The position they adopt - hanging beneath leaves, sheltered from rain - seems an ideal one from which fungal spores can disperse from the fungus-filled fly abdomen.

With the fly's rear end up in the air, facing outwards from the plant and down wind, it is difficult to imagine a better position for fungi of the future to begin life. Their deathbed position also involves their wings being spread apart and pressed downtowards the leaf surface. This, Dr Maitland thinks, is to prevent them from getting in the way of any sticky spores forcibly ejected by the fungus from the fly's abdomen.

But why do the fungus-ridden flies perch higher up on plants than their healthy siblings? Dr Maitland suggests it is because the spores can rain down on the healthy flies below, increasing the chances of infecting them and perpetuating the fungus.

The effect a flea has on its host's behaviour is well known and easy to understand. What is truly striking in the tale of the dungfly is how a primitive "plant" such as a fungus can so alter the physiology and behaviour of its host. No one knows the answer to that one.

When the same fungus, or a related species, parasitises the housefly, it does not change its host's perching position. Instead, infected housefly cadavers somehow become highly attractive to sexually active male houseflies. As the males try to mate with the corpses, they pick up a sort of venereal disease and so the fungus has a chance to disperse itself. The attraction of fungus-filled dead flies might be hard to imagine; perhaps some chemical attractant is involved. In the summer large numbers of houseflies succumb to this fungus. So if you see piles of dead houseflies, don't clear them up too quickly; leaving them for a while increases the chances of even more flies being killed - which means less swatting.

Arts and Entertainment
TV Review: Sabotage, a meltdown and, of course, plenty of sauce
newsVideo for No campaign was meant to get women voting
A photo of Charles Belk being detained by police on Friday 22 August
i100'Geography can be tough'
Louis van Gaal looks dejected after Manchester United's 4-0 defeat by MK Dons on Tuesday night
Actor, model and now record breaker: Jiff the Pomeranian
REX/Eye Candy
Down time: an employee of Google uses the slide to get to the canteen
scienceBosses are inventing surprising ways of making us work harder
Alexis Sanchez celebrates after scoring his first goal for Arsenal in the Champions League qualifier against Besiktas
sportChilean's first goal for the club secures place in draw for Champions League group stages
Arts and Entertainment
Amis: 'The racial situation in the US is as bad as it’s been since the Civil War'
booksAuthor says he might come back across Atlantic after all
ebooksAn evocation of the conflict through the eyes of those who lived through it
Life and Style
Google Doodle celebrates the 200th birthday of Irish writer Sheridan Le Fanu
Arts and Entertainment
Vinyl demand: a factory making the old-style discs
musicManufacturers are struggling to keep up with the resurgence in vinyl
In Eternal Sunshine of the Spotless Mind Jim Carrey and Kate Winslett medically erase each other from their memories
scienceTechnique successfully used to ‘reverse’ bad memories in rodents could be used on trauma victims
Arts and Entertainment
Singer Pixie Lott will take part in Strictly Come Dancing 2014, the BBC has confirmed
Travel Shop
the manor
Up to 70% off luxury travel
on city breaks Find out more
Up to 70% off luxury travel
on chic beach resorts Find out more
sardina foodie
Up to 70% off luxury travel
on country retreats Find out more
Latest stories from i100
Have you tried new the Independent Digital Edition apps?
Independent Dating

By clicking 'Search' you
are agreeing to our
Terms of Use.

iJobs Job Widget
iJobs General

Head of IT (Not-for-Profit sector) - Lewes / Brighton

£45000 - £50000 per annum + 5 weeks holiday & benefits: Ashdown Group: Head of...

PE Graduate?

Negotiable: Randstad Education Sheffield: Are you a PE graduate looking for a ...

Primary Teacher

£90 - £135 per day + travel expenses: Randstad Education Newcastle: Key Stage ...

Humanities Teacher

£100 - £150 per annum: Randstad Education Leeds: Permanent Teacher of Humaniti...

Day In a Page

Israel-Gaza conflict: No victory for Israel despite weeks of death and devastation

Robert Fisk: No victory for Israel despite weeks of devastation

Palestinians have won: they are still in Gaza, and Hamas is still there
Mary Beard writes character reference for Twitter troll who called her a 'slut'

Unlikely friends: Mary Beard and the troll who called her a ‘filthy old slut’

The Cambridge University classicist even wrote the student a character reference
America’s new apartheid: Prosperous white districts are choosing to break away from black cities and go it alone

America’s new apartheid

Prosperous white districts are choosing to break away from black cities and go it alone
Amazon is buying Twitch for £600m - but why do people want to watch others playing Xbox?

What is the appeal of Twitch?

Amazon is buying the video-game-themed online streaming site for £600m - but why do people want to watch others playing Xbox?
Tip-tapping typewriters, ripe pongs and slides in the office: Bosses are inventing surprising ways of making us work harder

How bosses are making us work harder

As it is revealed that one newspaper office pumps out the sound of typewriters to increase productivity, Gillian Orr explores the other devices designed to motivate staff
Manufacturers are struggling to keep up with the resurgence in vinyl records

Hard pressed: Resurgence in vinyl records

As the resurgence in vinyl records continues, manufacturers and their outdated machinery are struggling to keep up with the demand
Tony Jordan: 'I turned down the chance to research Charles Dickens for a TV series nine times ... then I found a kindred spirit'

A tale of two writers

Offered the chance to research Charles Dickens for a TV series, Tony Jordan turned it down. Nine times. The man behind EastEnders and Life on Mars didn’t feel right for the job. Finally, he gave in - and found an unexpected kindred spirit
Could a later start to the school day be the most useful educational reform of all?

Should pupils get a lie in?

Doctors want a later start to the school day so that pupils can sleep later. Not because teenagers are lazy, explains Simon Usborne - it's all down to their circadian rhythms
Prepare for Jewish jokes – as Jewish comedians get their own festival

Prepare for Jewish jokes...

... as Jewish comedians get their own festival
SJ Watson: 'I still can't quite believe that Before I Go to Sleep started in my head'

A dream come true for SJ Watson

Watson was working part time in the NHS when his debut novel, Before I Go to Sleep, became a bestseller. Now it's a Hollywood movie, too. Here he recalls the whirlwind journey from children’s ward to A-list film set
10 best cycling bags for commuters

10 best cycling bags for commuters

Gear up for next week’s National Cycle to Work day with one of these practical backpacks and messenger bags
Paul Scholes: Three at the back isn’t working yet but given time I’m hopeful Louis van Gaal can rebuild Manchester United

Paul Scholes column

Three at the back isn’t working yet but given time I’m hopeful Louis van Gaal can rebuild Manchester United
Kate Bush, Hammersmith Apollo music review: A preamble, then a coup de théâtre - and suddenly the long wait felt worth it

Kate Bush shows a voice untroubled by time

A preamble, then a coup de théâtre - and suddenly the long wait felt worth it
Robot sheepdog technology could be used to save people from burning buildings

The science of herding is cracked

Mathematical model would allow robots to be programmed to control crowds and save people from burning buildings
Tyrant: Is the world ready for a Middle Eastern 'Dallas'?

This tyrant doesn’t rule

It’s billed as a Middle Eastern ‘Dallas’, so why does Fox’s new drama have a white British star?