There are three varieties: larval Bearbugs, adolscents, and adult Bearbugs. All three move at an extremely slow crawl and may drop Dragonstone when killed.
Larval Bearbugs are the smallest and weakest, offensively and defensively; however, like the stronger varieties, they are virtually immune to fire damage. They attack by biting or hopping on the player. Unlike larger Bearbugs, they are capable of long-distance flight and can detect the player from a relatively long range.
Adolescent Bearbugs are noticeably larger than larvae and are much stronger offensively, although they have the same attacks for the most part. However, they can also charge at the player at relatively high speeds, often breaking the guards of smaller shields. Upon death, they will glow bright orange and emit a high-pitched whistle for two seconds before violently exploding; the blast radius is approximately equivalent to that of God's Wrath and deals severe fire damage.
Adult Bearbugs are several times larger than the player character and crawl at a speed of about half a pace per second. Their bite is even stronger than those of adolescents, although they lose the ability to charge or hop. Instead, their self-destruct explosion has about a fifty percent larger radius and is likely to kill or nearly kill just about any character caught in it. Adult Bearbugs resist physical damage to the point that the average weapon will have lost a quarter of its durability before the Bearbug finally dies; Poison is a safer option, but takes multiple "applications" and several minutes before actually killing the Bearbug, due to its high HP.