Crawling or swarming with creatures; full of things moving on the ground or surface.
From a- (on, in) + crawl, from Middle English crawlen, possibly from Old Norse krafla (to scratch or claw). The prefix a- makes it mean 'in a crawling state.'
Before we had 'creepy-crawlies,' people said 'acrawl'—it's an old-fashioned but vivid way to describe that itchy feeling of a surface filled with insects or bugs!
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