Even if digital scales are now used to sort fighters into weight classes separated by one-hundredth of a gram, cricket trainers still follow many of the rules and recommendations laid out in a 13th century how-to guide written by Jia Sidao, the Southern Song prime minister whose obsession with crickets supposedly led to the dissolution of the empire.

There is an elaborate system for feeding, judging matches and categorizing fight styles — “Creep like a tiger, fight like a snake,” describes one particularly effective move. The trained eye can supposedly differentiate 260 different grades and skin tones.

Although championship brawls take place after the fall equinox in late September, cricket season begins in earnest during summer, when farmers take a break from tending crops to thrash their way through corn fields after dark in the search for would-be gladiators.

Experts agree on one thing: the best specimens come from a few counties in northeastern Shandong Province, where the soil and climate seem to produce a particularly fiery breed. “The loudest chirpers are usually the fiercest,” said Chen Chuanfang, 47, a corn farmer from Ningjing County who estimates he makes an extra 10,000 renminbi a year from cricket fighting.

While some die-hards trek out to Shandong, most buyers scour Beijing’s main insect market in the south of the capital, where peasants display their specimens in ceramic jars capped by metal lids.

Serious trainers often purchase 200 or more males, at roughly 10 renminbi, or $1.60, a pop, with the hope of finding a handful of decent brawlers. Promising candidates might be given names like Yellow Flying Tiger or Big Purple Teeth.