European pine sawfly larvae

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Noticed these guys munching away on my mugo pines today. Happy to see they weren't winter moth caterpillars, but a bit concerned as there gangs of them. Turns out they are sawfly larvae, not technically a caterpillar (Lepidoptera) but apparently birds love to feed em to their babies, so I left them for a while. Interestingly, they only eat last year's needles, not new growth, to ensure that next year's larvae will have something to eat. Clever buggers!