Fingerlings, those colorful chirping monkeys (and sloths and unicorns) that wrap around your finger, have become one of the most desired toys on holiday shopping lists.

Unfortunately, the $15 creatures are sold out online almost everywhere.

But check eBay or Amazon, and sellers are offering them for double, triple and quadruple their original price. There is even one being advertised for $5,000.

“If it’s popular, it’s going to be taken by bots and resold,” said Omri Iluz, the co-founder and chief executive of the cybersecurity firm PerimeterX, in a phone interview.

The bots work by constantly pinging retail websites, searching for sales and analyzing URLs.

The moment an item is in stock, the software runs through the checkout process at a speed that is “completely inhuman,” said Iluz, whose company protects large retailers and other organizations from bot attacks.

The bots are drawn to scarce items and use web-scraping techniques to guess the ID of an unreleased product, PerimeterX explains on its website. That allows scalpers to buy products before an official sale becomes public.

Amazon said Tuesday that it monitors bot buying activity, and attempts to limit the purchase of high-demand products.

Target has also taken measures to deter resellers, said a company spokesman, Eddie Baeb, “including quantity limits for purchases and technologies designed to help us monitor and prevent reseller activity.”

On Sunday, Sen. Chuck Schumer, D-N.Y., tasked retail trade associations to take action.

“When it comes to purchasing products online, major retailers should put forth policies that will help prevent future Grinch bots from stealing the season’s hottest toys,” he said in a statement.

Unusual purchases ought to raise a red flag said Angelo Roefaro, a spokesman for Schumer.

“Say there’s a suspicious order placed — for example a massive quantity at extreme speed — they should be able to have some human intervention in that transaction and potentially block the sale,” Roefaro said in an email.

Schumer co-sponsored the Better Online Ticket Sales Act, or BOTS Act, which was signed into law last December, and is targeted at online ticket scalpers.

© 2017 The New York Times Company