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.

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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 4,000 wireline and wireless customers' phones to go 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 fiber-optic cables after shimmying through 2-centimeter-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.

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% 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 1% 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 fiber-optic cables in locations as varied as Ontario and India, leaving hundreds of thousands of customers without Internet or phone service.
  
  

• A data center 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 odor.
  
  

• 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 U.S. 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.