Sometimes an animal species seems so well-suited to California that it's hard to imagine it may not have been there in ages gone by. Fact is, though, we've added to California's bestiary quite a bit since the first European settlers arrived. There are a lot of "wild" animals in California who never would have been here if they hadn't gotten help from humans.

Some of the animal species we introduced, on purpose or by accident, have made themselves right at home in our cities and our wildlands. Some have seemed to fit in without causing obvious harm to other species. Others have caused serious damage to the landscape. Most of them fall somewhere in between.

Did you know that all of these animals were introduced to California? Some of the entries on this list may surprise you.

Opossums

Some people love them, with their nearly harmless demeanor, quiet habits, and ability to rid a vegetable garden of snails overnight. Others can't get past the snaggle-toothed grin and ratlike tail. Whatever your viewpoint, you may well have assumed that the Virginia opossum, Didelphis virginiana, with its primeval appearance, has been in California since time immemorial.

The truth is that there were no opossums in California before the 1890s, when a small population of the marsupial was moved to Los Angeles County, where their descendants spread across the South Coast. A second population was brought into San Jose from Tennessee in 1910 by migrants nostalgic for the wild food of home, and a third population of South Carolina opossums was released into the southern Sierra Nevada after a fur farming venture failed.

Between those three main introductions and a host of smaller ones, opossums have spread throughout California and the rest of the Pacific Coast. They have a supremely generalist diet, eating a range of foods from live lizards and snakes to rotting tree fruit, and that habit has allowed them to thrive in the widely varied habitats available to them in California.

That diet has probably also kept the opossum from becoming a walking environmental disaster, in that it doesn't seek out specific kinds of food such as the eggs of native birds, and it doesn't seem to have badly displaced other native animals through competition.

Eastern fox squirrels

Here's another animal that just "looks Californian," but isn't. The familiar eastern fox squirrel, Sciurus niger, was first introduced into California in the late 19th Century, and the landscape full of nut-bearing trees has encouraged their rapid spread.

The bad news is that depending on the kind of habitat they move into, eastern fox squirrels can displace a closely related California native, the western gray squirrel

(Sciurus griseus).

That's not true of every kind of habitat: as of 2009, the two species seemed to be coexisting in parts of Griffith Park. But in other places, the victory of eastern fox squirrels over their western cousins is inexorable. In 2005, biologists first noticed eastern fox squirrels on the Cal Poly Pomona campus, at the time a stronghold of western gray squirrels. By 2009 there were no gray squirrels left on campus.

Honeybees

They're in trouble nationwide as a result of a variety of factors, most notably pesticides. But it turns out that despite all the benefits they provide Californians, honeybees only made it here in 1853. That was thanks to a fellow named C.A. Shelton, who brought 12 hives around the Cape to California. All but one hive died before they reached their destination in the farm fields near San Jose. So did Shelton, in a ship boiler explosion on the trip's last leg between San Francisco and the bees' final landing in Alviso.

Honeybees are Old World insects, and the most commonly domesticated species, Apis mellifera or the European honeybee, probably originated in Africa, spreading across Europe and Asia and imported into North America in the 17th Century.

Shelton's first California hive prospered, and was followed by others. Now, European honeybees are crucial to the Golden State's agricultural sector, and we regard their future with fear. Ironically, the presence of introduced honeybees may be suppressing populations of native bees, which you don't hear much about in the "save the honeybees" brochures.

Parrots

They're a near-ubiquitous sight in parts of Los Angeles, San Francisco and other coastal cities. They seem to fit in well with the tropical fruit trees and palms: a brilliant and very loud part of the urban landscape. But it'a hard to find records before 1960 of any of the 13 species of parrots now known to have stable populations in California cities.

And unlike opossums and honeybees, those who brought parrots to the state and released them didn't keep public records. That's probably because the raucous birds now caucusing in the queen palm down the block descend from either escaped pets or other fugitives from the captive parrot trade.

One species of parrot, the monk parakeet or Quaker parrot, was deemed such a potential threat to California agriculture that its importation and possession has been banned in the state, and the California Department of Fish and Wildlife describes an eradication campaign against the species as a success. Other species haven't turned out to be quite so disruptive, focusing on non-native food sources like urban fruit trees and taking time out to star in the occasional documentary film.

Bison

The symbol of Wild America probably didn't exist in most of California in the 17th Century, though there's some dispute over whether herds of plains bison may have occasionally ranged into a thin sliver of the state in eastern Modoc County back in the day, likely staying in the desert steppe east of the Warner Mountains.

That may come as a surprise to visitors to Santa Catalina Island, where the local bison herd seems to blend wonderfully into the landscape.

But aside from the possibility that those eastern Modoc bison may have visited once in a while, and aside from a couple vague second-hand reports of "buffaloes" related by early California explorers like Juan Crespí, there is essentially no evidence of modern bison in California.

It kind of makes sense: bison don't climb steep mountains if they can avoid it, and California is well-defended along its eastern border with steeply tilted fault-block mountain ranges. Why cross the Warners when there's perfectly good grass in the sagebrush steppe below?

Of course that's modern bison, with the easy to remember Latin binomial "Bison bison." There were other species of bison in California back in the Pleistocene, even bigger and crankier and more dangerous than the kind we have now. Bison antiquus, the most common large herbivore found in the La Brea Tar Pits, lived here up until about 10,000 years ago. Bison latifrons, which had a truly fearsome set of horns that could span seven feet from tip to tip, died out in California somewhere between 30,000 and 21,000 years ago.

But their inheritors the modern bison? Not so much with the California territory. Something to remember as you take in the iconic California countryside on Catalina.