A little knowledge of natural history is a dangerous thing. This is, first, because knowing a few things — the names of some common wildflowers, or the songs of some neighborhood birds — begets curiosity about more things, and soon enough you’ve gone from installing an identification app on your smartphone, to ordering a field guide, to pricing binoculars. But, second, it’s dangerous because once you know a little natural history, you start to notice living things are often not where you expect them.

Should the violet-blue flowers of a jacaranda really be shading the upper slopes of the Griffith Park ridgeline, overlooking the urban sprawl of Los Angeles? Can that really be an eastern gray squirrel chattering at you from the bushes in suburban Seattle? Why on Earth is a honeybee visiting the flowers of a Joshua tree, which offer no nectar and very little pollen?

The most immediate answer for all of these is, because humans put them there. Jacarandas and eastern gray squirrels and honeybees are just some of the species we’ve carried to new habitats for our own purposes. But in all three cases these organisms are not going about human-directed business — they’ve gotten away from the places they were introduced, to make a living on their own terms. And the questions they prompt apply much more broadly.