Coloring books for adults are flying off shelves : At the moment, five of the top 30 titles on Amazon’s best-seller list are coloring books aimed at adults.

The Boston Globe reports:

As merchandise manager at Barnes & Noble’s Burlington location, Tracy Moniak has a particularly good vantage point from which to track the ebb and flow of literary trends.

She knows, for instance, that history books do well around Father’s Day. That cookbook sales pick up around the holidays. And that graphic novels are once again gaining steam.

But the recent explosion — and it really is an explosion — in popularity of coloring books for adults? “I did not see this coming,” said Moniak.

In a sudden, unexpected, and generally curious development, grown-up versions of the doodle-books used by countless kindergartners have not only become a thing — but the thing, as far as millions of rapt Americans are concerned.

At the moment, five of the top 30 titles on Amazon’s best-seller list are coloring books aimed at adults. Barnes & Noble currently carries well over 100 different adult coloring book titles, many of which feature much more intricate and detailed designs than children’s versions. And as the trend seeps into the mainstream, publishers and booksellers have been left scrambling to keep the most popular titles on store shelves.

No word yet from Stanley , the expert on adult-baby regression, on this story.