Strange Animal 'Alliances' That Scientists Are Still Struggling To Explain

Most animals tend to stick to what they know when it comes to getting by, but only the cleverest of creatures understand that two heads are always better than one. Whether for convenience, necessity, or just plain fun, these unusual animal "alliances" are giving a handful of creatures a leg up on their competition — and leaving scientists completely baffled.

1. Sea Urchins And Carrier Crabs

When carrier crabs travel from one place to another, sometimes they feel the need to bring along some extra protection. These crabs will use their back legs to pick up a sea urchin and hold it over their head. The spines keep the crabs safe and the slow sea urchin gets a speedy trip to a new feeding area.

2. Plover Birds And Nile Crocodiles

Did you know that Nile crocodiles have their own avian dentists? When they have something stuck in their teeth, they'll hold their mouths open until a plover bird stops by. The bird picks bits of dead animals out of the crocodile's mouth for a meal and the croc's teeth avoid infection.

3. Zebra Swallowtail Butterflies And Pawpaw Trees

Pawpaw trees grow across the eastern U.S. and Canada and are known to produce a tasty fruit with yellow flesh and enormous black seeds inside. This makes the pawpaw the perfect habitat for zebra swallowtail butterflies, as their caterpillars eat the leaves of these trees while simultaneously helping to induce pollination.

4. Oxpeckers, Rhinos, and Zebras

On the Saharan plains, tiny white birds land on the backs of rhinoceroses and zebras grazing on the grasses. These oxpeckers nibble ticks, fleas, and any other bugs off the large herbivores. Yet this relationship is a little one-sided: if the animals have open sores, the oxpeckers will drink their blood like vampire birds.