The crime scenes last February in rural Sweden looked remarkably similar despite being 90 miles apart. The perpetrators appeared to have entered through the smallest of cracks. Footprints dotted the snow. Each case claimed more than a thousand victims.

And then, there were the telltale teeth marks.

No doubt about it: Field mice had done the dirty deeds.

TeliaSonera, a Stockholm telecom carrier, suffered two nearly daylong network outages that caused roughly 4000 wireline and wireless customers' phones to go as quiet as, well, the mice. The company squarely laid the blame at the tiny paws of rodents that the Swedes call sorks.

The outages were maddening in that they were caused by the animals gnawing through fibre-optic cables after shimmying through 2cm-wide gaps between cement valves and locks designed to protect the phone lines from animals and forces of nature, says Arne Duvberg, chief technician at Flextronics Network Services, a company that maintains TeliaSonera's networks in the region.

And don't even get him started on birds.

"We have to send out service men on a daily basis to take care of the damage being made by the woodpeckers," he says.

Nature vs network
TeliaSonera by far wasn't the first network operator to get caught in a mousetrap and won't be the last. Just how common animal attacks on networks are, though, is hard to pinpoint. One estimate, cited by author Robert Sullivan in his 2004 book Rats (in which he monitors a New York City alley for a year), is that 18 percent of all phone-cable disruptions are caused by rats. But others say the frequency of animal-related damage is much lower. AT&T, for example, figures less than one percent of all its outages are caused by rodents.

Despite the shortage of statistics, anecdotal evidence of nature vs network run-ins abounds:

- In the past few years, rats have been blamed for chewing through fibre-optic cables in locations as varied as Ontario and India, leaving hundreds of thousands of customers without Internet or phone service.

- A data centre at Stanford University in the mid-1990s switched to back-up generators after a squirrel blew out the main transformer. The rodent's charred remains were found hours later, exposed by its pungent odour.

- Texas Tech University researchers have cited red, imported fire ants as being network troublemakers as far back as 1939, when Southwestern Bell Telephone reported problems in Galveston, Texas.

- AT&T and other telecom companies and equipment makers seeking ways to protect their networks and products from pocket gophers' choppers drew fire from animal rights activists in the mid-1990s for paying US government researchers over two-plus decades to trap the animals, cage them and watch them gnaw on cables strung within the cages. Such cable-durability tests have since been halted.

- Owners of underwater cables have had to make their links shark resistant after suffering outages caused by fish bites.

Rodents are considered especially threatening to network cabling.

"Rodents and wire damage go hand in hand," says Bobby Corrigan, a pest control expert in Indiana who calls himself an urban rodentologist.

And it's not that the animals are bent on having a high fibre-optic diet, either. Eric Spinner, pest control operator for Maven Pest Management in New York, explains that rodents gnaw on wires and other chewable objects to grind down their incisors.

"Failure to do so will allow them to grow long and actually occlude their lower jaws to the point where they can't open their mouths to eat," he says.

Get protected
Telcordia, which crafts specifications used by carriers and equipment makers, tests for the hardness of cables and equipment enclosures, and recommends cabling be protected in covering with at least a 1- or 2-inch radius to prevent certain animals from wrapping their jaws around it.

Ernie Gallo, director of telecom services at Telcordia, says the increased use of fibre-optic cabling has forced carriers to pay more attention to network protection, given that the outage of a single fibre connection can mean many more businesses and individuals will be affected than they will when they are old copper links go down.

Protecting networks from animals isn't only about keeping up communications links. It's also about safeguarding field technicians who work on the lines. Requirements are followed in designing equipment enclosures that are meant to keep insects such as wasps from building nests within them, Gallo says.

Efforts such as covering cables with pepper spray have been made over the years to discourage cable-chewing, Gallo says. Although he emphasises that sticking to the basic Telcordia specifications can greatly reduce, if not eliminate, animal interference.

Jay Adelson, CTO and co-founder of Equinix, a provider of data centres and Internet exchange services, says a massive rodent-eradication program is one of the first things his company does when building a data centre.

"We make sure we quarantine off the building with steel walls and find any point of entry and seal it up," he says.

While outside cabling is commonly sheathed in metal to avoid animal or other damage, armouring cable within a data centre can greatly limit the flexibility of cable that might need to be moved often, he cautions. Cabling company experts also say that armouring wires can as much as double the cost, so careful risk vs. cost assessments must be done.

Stuart Aust, for 15 years the owner of Bug Doctor in New Jersey, says his company has helped to protect enterprise networks by putting bait stations outfitted with "rodentcide" under raised floors in computer rooms. "We provide a deodoriser as well," he says, for those cases where rodents die and aren't discovered right away.

Of course, even the best efforts to animal-proof networks aren't always successful.

"Data centres might seem secure, but if there is any hole - if you can put a pencil through it - then a mouse can get through it," says Greg Baumann, technical director for the National Pest Management Association.

A comfy home for pests
Data centres generally provide three things rodents need: food, water and safe harbour. "While companies might not encourage bringing food into these climate-controlled spaces, there is always the leftover birthday cake or emergency granola bars," he says.

And once critters get into a data centre, even armouring cable will not necessarily stop them from damaging wires or getting into electrical systems that power networks, says Steven Elmore, an applications engineer with cable maker CommScope.

"It will just slow them down," he says. "I've actually seen armoured cable chewed through."

New animal control methods are always in the works, says Michael Conover, director of the Berryman Institute, a US organisation focused on resolving human-wildlife conflicts.

"We have been doing research on impregnating a rodent repellent into the plastic covering of cables," he says. "While this approach works in the short-term, it is too early to tell if it is a long-term solution."

You might think the shift from wire-based to wireless networks might give animals less to chew on going forward, but that's not necessarily the case. "There are still a lot of wires in wireless networks," CommScope's Elmore says.

Meanwhile, network professionals say it actually isn't the rats, ants and gophers that have them most concerned. When Flextronics' Duvberg was asked to point out the most harmful animal he answers quickly: "Homo sapiens. When an excavator causes problems, one thing is for sure: The problems are big."