Last week came word that construction of the far-off Central Subway project may be displacing an urban rat army. But before freaking out completely (and just slightly after reading the Wikipedia entry on rat kings), we decided to follow up with someone beyond the Chron's one-man civilian witness. We reached out to Dr. Robert M. Corrigan, an Urban Rodentologist from RMC Pest Management Consulting, for answers to our burning rat-related questions. Here's what we learned.
On SF's rats in general: "There are two species of urban rats that live in San Francisco; 1) the Norway rat (or brown rat); and 2) The roof rat (or black rat). If construction impacts the rats below ground, it is usually the ground dwelling Norway rat (weight about 10-16 ounces; length about 16 inches including the tail). The roof rat weighs about 8-12 ounces and is about the same length as the larger Norway rat because its tail is long. This rat, if present in a building, is usually in the upper stories. If the building is taken down, they will disperse. They also live in tall palm trees, thick bushes along the fences, etc. If major construction tears down bushy vacant lots, etc., this rat can be displaced)."
The good news: "There are no 'super rats' from deep deep below the city; nor any super rats emerging as a result of climate change (at least not in this early stage in the game)."
The bad news: There are rats that live in palm trees (!), and someone (perhaps a rat insider?) just spent $450,000 to put thirty-odd palms along the new Bay Bridge span. Hello rat condos with a view.
On the effects of construction on rat populations: "The thought of dark tunnels below are cities conjures up images of millions of rats which will 'go running' all over the streets and into everyone's homes and businesses. The reality is there may be cases of some jackhammers, tunnel boring machines (TBMs), explosions etc, that will displace some rats in some blocks ; and these rats will scatter to wherever they can feel safe again. But the rats have to already exist in those areas prior to the beginning of any construction for them to be 'disrupted', i.e., construction alone does not cause rats. When populations of rats naturally increase but coincide with the onset of large scale construction projects, the construction projects are always, always, blamed for 'causing rats.' The public has an image of thousands of rats living in large mega-colonies way down below the city and being scared up to the surface."
The good news: So, large mega-colonies of rats running their own complex societies deep below the streets don't exist? Excellent.
The bad news: We're just not sure we can believe that.
On what we don't see: "Typically, prior to the beginning of any construction, city rats are already thriving at the street level in those parts of a city where sanitation is poor; in peoples backyards, under their stoops, beneath a dog house in the yard, in the building's basement walls, in poorly maintained parks (e.g., overflowing litter baskets); beneath the everyday sidewalk, in old sewer lines of the city, along the wharf areas in the rip-rap; in burrows hidden in the grass nearby the ordinary dumpster behind the fast food restaurant, etc. All these rat populations fluctuate up and down depending upon how much human food waste and harborage we allow the rats in these areas. But because rats are most active at night, when most humans are indoors and/or sleeping, they aren't aware of the low levels of rats living very close by."
The good news: Humans are usually asleep when the majority of rats come out to play, and so anecdotal evidence of rat armies, while exciting for humble news organizations such as ourselves, are probably not representative of the full situation.
The bad news: Rats are already freaking everywhere. Everywhere!