**Kermes Scale** (genus *Kermes*) are a group of specialized **soft scale insects** that infest **oak trees** (*Quercus* spp.). They are easily overlooked because the adult female scales look like small, spherical, plant galls or tiny balls of bark rather than insects. They feed by sucking sap from the twigs and branches. While they rarely kill a mature tree, large infestations cause severe aesthetic damage, including branch dieback, leaf yellowing, and heavy fouling of the lower canopy and ground with sticky **honeydew** and black **sooty mold**.
Taxonomy and Classification
Kermes Scale belongs to the order Hemiptera, family Kermesidae. They undergo incomplete metamorphosis. They are closely related to the traditional soft scales but are distinctive due to the hard, gall-like, shell-shaped body of the mature female. The female remains stationary, feeding and laying eggs under her protective body. The name *Kermes* derives from the ancient use of certain species to create a rich red dye.
Physical Description
Adult female Kermes scales are spherical and stationary, 1/8 to 1/4 inch in diameter.
- **Appearance (Key ID):** The female appears as a smooth, round, shiny brown or dark brown ball, often looking like part of the oak branch.
- **Location:** They are found fixed to the bark of young twigs and small branches of oak trees.
- **Crawlers:** The active, mobile first instar nymphs (**crawlers**) are minute, yellowish, and mobile for only a short period as they seek a permanent feeding site.
- **Damage Sign:** Abundant **honeydew** dripping from the canopy, black **sooty mold** growing on the honeydew-covered leaves, and dieback of small twigs (flagging).
Distribution and Habitat
Kermes Scale species are native to Europe, North America, and parts of Asia, wherever oak trees are dominant. Their habitat is specifically the twigs and branches of oak trees, favoring young trees or those that are stressed. They often colonize the lower, inner branches first.
Behavior and Conflict
The conflict is aesthetic damage and plant stress.
- **Honeydew Nuisance:** Large populations create a copious amount of honeydew, which drips onto anything below the tree (decks, cars, patio furniture), making a sticky mess and promoting sooty mold.
- **Sap Draining:** Heavy feeding can significantly stress the tree, leading to premature leaf drop and twig mortality (flagging), which, over many years, can weaken a tree.
- **Ant Association:** Ants are attracted to and often protect the scale insects from natural predators in exchange for feeding on the honeydew, complicating natural control.
Management and Prevention
Control is integrated pest management (IPM), with a focus on systemic treatment and crawler control.
- Control is most effective when targeting the vulnerable **crawler stage** (timing varies, typically late spring/early summer).
- For small, localized infestations, prune and destroy infested twigs and branches.
- **Horticultural Oil:** Apply **dormant oil** (before bud break) to smother the overwintering scales.
- **Systemic Insecticides:** Apply a systemic product (often a neonicotinoid) as a soil drench or trunk injection, which the tree absorbs and delivers to the feeding scale. This is highly effective against soft scales but should be timed to minimize risk to pollinators.
Conservation and Research
Kermes Scale is managed as an ornamental pest of high-value shade trees. Research focuses on conserving and augmenting the natural enemies (parasitic wasps and lady beetles) that attack the scale, and improving the delivery methods for systemic insecticides to large oak trees.