Picture this: you’re out hiking through a misty rainforest. After brushing aside some foliage, your heart leaps when a huge, powerful constrictor slithers by. Since the world’s most heavily-built snake species are all either boas or pythons, this reptile probably belongs to one of those groups. But how can you tell them apart? And from which family does “your” serpent hail?

Before breaking out the field guide, take geography into account. While pythons are Old World snakes, boas also dwell in the Americas. Note, however, that human globalization has helped many species artificially spread out and invade distant lands. For instance, just when everyone thought Florida couldn’t get any wilder, the enormous Burmese python (Python molurus bivittatus) began populating the Everglades during the 1980s, thanks largely to irresponsible pet owners.

Another decent rule of thumb is reproduction. Boas tend to bear live young, whilst all known pythons are egg-layers, with gravid mothers sometimes squeezing out over two dozen in a single clutch. Also, the two families sport slightly-different body plans. In pythons, but not boas, a pair of upper jaw bones called the “premaxillabear teeth.

At this point, you might be wondering where anacondas fit into all this. Well, these magnificent South American creatures belong squarely to the boa camp—in fact, they’re sometimes called “water boas.” Anacondas, like all king-sized constrictors, are great at snagging headlines. Yet, such giants are just the tip of the iceberg, for boas and pythons come in a wide range of shapes and sizes. True, the enormous reticulated python (Python reticulatus) can exceed twenty feet in length. The wee anthill python (Antaresia perthensis), meanwhile, usually attains a child-like twenty inches.

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Despite all the differences we’ve laid out, several boas and pythons occupy identical roles in their respective habitats. That handsome critter pictured above is an Aussie native called the green tree python (Morelia verdis). Half a world away lives South America’s emerald tree boa (Corallus caninus), which you can check out in the photo below.

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No, you’re not seeing double. Genetically, these aren’t close relatives: boas and pythons appear have been taking separate evolutionary paths for quite some time now. Nevertheless, their similarities are uncanny. Both dangle from tree branches while waiting for prey, both reach a maximum length of roughly six feet, and both start out as either red or yellow youngsters before turning into vibrant green adults.

This phenomenon’s called “convergent evolution,” a process whereby unrelated organisms independently evolve comparable traits as they struggle to adapt to similar niches or environments. Ain’t nature incredible?