The Echidna's Incredible Expanding Testicles

The echidna is a pretty strange mammal. Most notably, it is the only mammal other than the platypus that lays eggs. I've discussed in an earlier post why that doesn't disqualify it from being a mammal, but it is undeniably unusual. It's not even the only odd thing about echidnas, since they can also sense electricity through their snout, and the males have a four-headed penis.

I'm not making this up.

There are, in fact, four different species of echidna. The one most people are likely familiar with, though, is the short-beaked echidna (Tachyglossus aculeatus), on the grounds that it's the only one found in Australia. (The others, if you're wondering, live in New Guinea). In fact, they're found pretty much across the whole of Australia, albeit generally in open woodland or rainforest, rather than true desert. Even so, that's a fairly broad range of habitat types and variations in climate, and their behaviour does change somewhat across the continent.