I think there are a few animals that might serve as an answer to this question (for example the snow leopard). But one of the most elusive animals in the world is the Giant Squid, which lives in the deep ocean and can reach 13m in length! I might be biased, because I study squids. 🙂 Very few people have been lucky enough to observe one!
I think it would be hard for me to top Anthea’s answer as we learn about the Giant Squid mostly through finding their beaks (yes squid have beaks) in Sperm Whales which are their predator and not the easiest thing to find either (despite being the largest predator to have ever existed!).
However the spade toothed beaked whale (which doesnt have a real beak or even a spade!) is my bet for hardest animal to catch. We thought it was extinct until one washed up on a beach and that was the first time a full animal was seen (teeth had washed up before). To this day no one has seen a live spade toothed beaked whale!
There are, in fact, plenty of animals that are super difficult to catch… so difficult to catch that we only know them through a couple of videos, bones, or a few old specimens caught a long time ago… Anthea and Kevin already gave you some excellent examples. We could add thousands of bugs and reptiles that are known through just a single specimen ever caught.
We still find thousands of new species every year around the world. They live everywhere! I even have a friend who found a new species of wasp in Ireland a few years ago!
Lot’s of brilliant answers from the other scientists here! There are lots of animals in the sea and on land that are very difficult (or maybe even impossible) to catch.
I’ll just add one example from my fieldwork in Indonesia. A species of Dwarf Buffalo lives in the rainforest over there. I know, a dwarf buffalo living in a forest; it’s very strange! The locals call them Anoa and they are very, very difficult to see. Sometimes we would find there tracks, and people would set camera traps to try and photograph them but we never saw any. I find it amazing that a buffalo can live in a forest and remain unseen! If we can fail to see such big animal like that, what else are we missing?
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