A beastly sighting - a bag moth caterpillar

There is always something new to learn.  Today I saw something unexpected and unfamiliar - and, I confess, I found it quite unattractive and a bit disturbing at first - maybe because I didn't know how to regard it.  Was it a benign beast or was it more sinister?  Maybe its distinctive colouring was suggesting "don't mess with me!"  (Often brightly coloured caterpillars are advertising to predators that they are poisonous or unpleasant to eat - they don't need to try and hide to survive.)  Or maybe it was just that it took me by surprise and I was sure it was up to no good on my dwarf almond tree - although it was actually just hanging onto a green garden stake, and moving up it ever so slowly.

But soon enough it emerged again, just the first few segments stretching out then pulling the long brown bag up a small distance, then stretching out again. 

Thus it gradually climbed the stake.

When I went to check it later, it had disappeared.  By then I had figured out it was a bag moth caterpillar.  There are many different bag moths and many styles of bag decoration/camouflage, and while the male bag moth has wings the females are wingless and often don't leave the larval case.  They tend to have tough eggs, usually left in the protection of these tough bags.  While this sounds like a smart strategy, they are often subject to parasitic attack.  Nothing's perfect.  In this case the bag had an almost felted appearance, with little decorative bits of plant and twig.  It reminded me of homespun fibres.  Which it was, and it was a spun home too.