(Image: Mark Atwood via Flickr)

On a recent evening I was waiting for friends to disentangle from a crowded bar on 10th. In a slight haze, I tuned out the nightlife and looked around. Almost immediately I saw a shadow dart between a crack in a building and a dumpster. Several more zipped by, hugging the wall to a pile of refuse that had spilled behind the nearest establishment. Soon squealing erupted from the pile and two of these shadows bounced around on the edge of the garbage. I couldn’t help but shudder. I was watching rats.

When I say rats, I specifically mean those we’ve inadvertently spread across the world with our boats and planes. There are native rats in Washington, just not in your attic or on the streets of Pike and Pine. Being a major port, we are “lucky” to have two non-native species that grace our urban environment, both the Black Rat (Rattus rattus) and the Brown Rat (Rattus norvegicus).

Most of us are familiar with Brown Rats, as they’re the larger, dominate species. You may call them Norway Rats (it was once believed they were native to Norway when they showed up on ships in England), or maybe a Sewer Rat (referencing their habit of using our underground labyrinths as homes). Lab and pet rats are descendants of the wild Brown Rat but no one is totally certain of the species’ native home, except that they started to appear in Europe around the time trade with Asia began. Now they are on every continent excepting Antarctica (but boy are they close).

They can be frightfully large, 20 inches including the tail, large enough to incite panic in most. Brown rats burrow, which is why we find them in our crawl spaces, basements, and in the myriad forgotten holes we’ve created in developing a city. And, to top it all off they’re prolific breeders in those good habitats (temperate places with food and water aplenty). Females reach maturity at 5 weeks, gestate for 21 days, and then regularly have litters of 7 or more throughout the year. That’s a lot of rats.

The smaller Black Rat (at most around 10 inches long total) similarly originated in (Tropical) Asia and hitched their way around the globe on early trade ships. In the game of expansion they’re less aggressive than Brown Rats, but have held on in major ports in the US. While Brown Rats like to burrow, Black Rats like to climb, which is why they’ve been given the name Roof Rat. They will happily take up residence in your attic.

Rats below. Rats above. Great.

Rats populations thrive with access to food and water. Lack of water appears restricting but, what really brings all the rats to the yard is food. We leave food everywhere, even when we think we’re being clean. Rats will happily burrow into garbage to eat the tail of a burrito you tossed. Anything we eat, rats probably will too.

No one like’s to think about these things, which is why we don’t hear too much about rats. Most infestations are kept quiet (for good reason) and I’m not writing this to coach you on how to deal with a rat problem. In the challenging environment we’ve created for most species, it’s amazing rats thrive and it’s ironic that species we appreciate on the hill, like Barred Owls and Red-tailed Hawks, likely persist on them. Rats may not be deterred by the average house cat but they’re good prey for wild predators.

The bottom line for us in of the biological story of rats is that they’re vectors for many diseases (over 50 have been counted, but most notably hosting fleas that carry bubonic plague). I would never suggest we should attempt to co-inhabit peacefully, despite wanting people to appreciate them as fascinating living creatures. I definitely know how irrational rats can make us: At age 5, I woke up to find my father trying to deal with a rat by smashing it with a hammer. I also know how smart, fun, and affectionate a pet rat can be: I had two as a child. That still doesn’t stop my skin from crawling when I see them climbing through garbage. Rats are kinda gross, but that’s part of their success, because they’re willing to live on our margins. Regardless they’re still part of our urban natural history.