Bonus Pest Chance

is a Stat that increases the chance for multiple Pests to spawn at once.

Every is a guaranteed additional Pest spawn, while the leftover that is less than 100 is a percent chance for one more Pest to spawn.

Increasing Bonus Bonus Pest Chance

 * -|Pets=

Pets

 * -|Accessories=

Accessories

 * -|Enchantments=

Enchantments

 * -|Consumables=

Theoretical maximum
This totals to a maximum, which means at least 3 Pests will spawn at once every time, and there is a 80% chance for a 4th one to spawn as well.
 * (at nighttime)

Trivia

 * During testing on the Alpha Hypixel Network, allowed an option to prevent a Pest from spawning during Jacob's Farming Contests.