Ready, set, reverse!

Our cats really love to sit on the counters in our bathrooms. Every morning, as I’m getting ready for work, our older cat will come and sit on the counter for a few minutes – until I pull out the hair dryer, that is. The noise of this machine always scares her, and she inevitably jumps down off the counter and scampers away. A few days ago, however, she tried a new technique for getting off the counter. Instead of turning around and jumping down, she simply backed herself right off the edge. Not surprisingly, this didn’t work very well – she misjudged where the counter ended, and wound up with her rear legs in the trash can and her front legs on top of the toilet seat! (I guess I should be glad she didn’t wind up with her back legs in the toilet bowl.)

Now, I must admit, I laughed quite a bit at her predicament. (After making sure she as unhurt, of course.) But it sparked a question in my mind. She can back up quite well, but apparently she has to be level ground. And I wondered if that was a trait that all animals share. Can any creature that walks forwards also walk backwards? Or are there animals in the world that are physically unable to back up?

For the most part, animals that can walk forwards can also walk backwards. However, it is not universally true.

The one mammal that I came across that is unable to back up is the kangaroo. Kangaroos are marsupials that belong to the family Macropodidae, which means big feet. Other macropods include wallabies, quokkas, pademelons, honey possums, and wallaroos – in fact, there are over 50 different species of macropods. The most obvious difference between kangaroos and other species like wallabies and wallaroos is size. The 6 largest marsupial species are all referred to as kangaroos. In addition to really big feet, kangaroos have very powerful leg muscles, a strong tail for balancing, and a skeletal structure that makes them very efficient hoppers. But it also means that they can’t really walk. If a kangaroo has to move slowly, it forms a tripod between its tail and two forelimbs. You might see a kangaroo in this position if it’s eating something from the ground. But for general locomotion, hopping is much more efficient. And apparently if a kangaroo wants to retrace its steps (its hops?) it must turn around to do so. They cannot hop backwards, nor can they mince backwards in their tripod walk.

It has also been reported that certain birds are unable to walk backwards – in particular, ostriches and emus. These are the two largest birds on the planet; they are both members of the most primitive of modern bird families (including kiwis, cassowaries, and rheas). Both flightless, these guys rely on good old-fashioned leg power to get themselves around. Emus, in particular, can be quite speedy – they can sprint upwards of 30 miles an hour! They have a unique structure to their pelvic bones and muscles that allow them to move so quickly. They also have extremely powerful legs - in fact, emus are also the only birds that have calf muscles. Not only can emus run really quickly, their strong legs make them incredible jumpers. If startled, they can jump straight up almost 7 feet – which, considering that the bird itself is over 6 feet tall, is quite impressive. So they can move really well going forwards – but can they reverse? Unfortunately, though that statement is often thrown around as fact (and is even the title of a book – “Emus can’t walk backwards: Another round of dubious pub facts”), I wasn’t able to find any reliable source to tell me whether or not it was true. The evidence is mostly anecdotal. I guess the next option to me to verify this fact would be to camp out at the emu section of the local zoo and watch them for a few days to see if I can see any of them go backwards!

There may be other animals that cannot reverse their locomotion. One other suggestion my husband came up with was the centipede. With that many legs, I can imagine that it might very well be difficult for organize them all to go in reverse!

Anyone have any other ideas?