Some things just aren’t as they seem. This statement is true in almost every aspect of life. This is especially true when it comes to identifying insects.

Recently, a client brought in some river birch leaves infested with insects she needed help identifying. At first look, the insects were thought to be mealybugs because of the excessive amount of white, waxy residue found on their exteriors. However, once some of the residue was removed, it was obvious the insects in question weren’t mealybugs. The insects in question had pear-shaped bodies with cornicles (backward-pointing tubes that act as pores) present on their backs. These insects were spiny witch-hazel gall aphids (Hamamelistes spinosus). They are also known as river birch aphids.

Spiny witch-hazel gall aphids Hamamelistes spinosus. — Spiny witch-hazel gall aphids *Hamamelistes spinosus*. Photo Credit: Sherrie Smith, University of Arkansas System Division of Agriculture Cooperative Extension Service

Spiny witch-hazel gall aphids don’t do serious harm to healthy river birch trees, but they due cause aesthetic injury. Their feeding causes new leaves to develop irregularly. Like other aphid species, spiny witch-hazel gall aphids produce honeydew (sugar liquid) which attracts ants. The honeydew also provides a food source for sooty mold to develop.

Sooty mold on river birch leaves. Photo Credit: Matt Lollar, University of Florida/IFAS Extension – Santa Rosa County

Spiny witch-hazel gall aphids have an interesting life cycle that requires two hosts over the course of two years. They lay eggs on witch-hazel trees in the summer that hatch the following spring. The nymphs feed on flower buds causing spiny galls to form. The next generation of aphids develop inside the galls, then break away and fly to river birch trees. These winged aphids give birth to a new generation that resemble scale insects that overwinter on river birch trees. These scale-like aphids feed on newly forming leaves the following spring causing distorted leaves.

River birch leaf damage from spiny witchhazel gall aphid. Photo Credit: Matt Lollar, University of Florida/IFAS Extension – Santa Rosa County

Fortunately, the spiny witch-hazel does not usually cause enough harm to trees to warrant insecticide application. However, if their damage is too unsightly applications of insecticidal oil or imidacloprid at bud-break in the spring provide good control.

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Aphids on River Birch