What Insects Like Goldenrod: Plant Galls and Leaf Mines

What insects like goldenrod? A direct answer

Many insects like goldenrod (Solidago spp.), but the most conspicuous evidence of their presence are plant galls and leaf mines. Galls are abnormal growths on stems, leaves, or buds caused by insects such as gall midges, gall wasps, and tephritid fruit flies. Leaf mines are the trails or blotches inside leaves created by the larvae of small flies, moths, and beetles. Common gall-making insects on goldenrod include the goldenrod gall fly (Eurosta solidaginis), the goldenrod bunch gall midge (Rhopalomyia solidaginis), and various gall wasps. Leaf miners on goldenrod are often tiny flies in the family Agromyzidae or moths like Phyllonorycter species. These insects use goldenrod as a host plant, providing food and shelter for their larvae.

Understanding plant galls on goldenrod

A plant gall is an abnormal outgrowth of plant tissue induced by another organism, usually an insect or mite. On goldenrod, galls are often spherical or spindle-shaped swellings on stems, or a cluster of small leaves forming a rosette at the stem tip called a bunch gall. The insect larva lives inside the gall, feeding on the plant tissue and gaining protection from predators and weather. Galls can be caused by gall makers such as flies, wasps, moths, and beetles. On goldenrod, the most well-known gall is the ball gall created by the goldenrod gall fly. The adult fly lays an egg in the stem, and the larva secretes chemicals that cause the plant to grow a spherical gall around it. The larva overwinters inside, emerging as an adult in spring. Other galls include the elliptical gall and the bunch gall, each caused by different species.

Common gall makers on goldenrod

When you encounter a goldenrod gall, you can gently cut it open to see the larva (if you have permission and are careful not to harm the plant excessively). Many gall makers have specific host preferences, so the goldenrod gall fly is only found on certain Solidago species. The presence of galls is a sign of a healthy insect community, and these insects are an important part of the herbivore food web, providing food for birds like chickadees and woodpeckers, which peck open the galls to extract the larvae.

Leaf mines on goldenrod: a different kind of herbivory

A leaf mine is a tunnel or blotch inside a leaf caused by a larva that feeds on the internal leaf tissue between the upper and lower epidermis. Leaf miners are typically the larvae of small flies (Diptera), moths (Lepidoptera), or beetles (Coleoptera). On goldenrod, you may see serpentine mines that wind like a ribbon, or blotch mines that form irregular patches. The pattern of the mine often helps identify the insect species. Common leaf miners on goldenrod include agromyzid flies such as Liriomyza and Phytomyza species, and small moths like Phyllonorycter species. Leaf miners do not form galls, but they are still considered herbivores. Often the adult insect is a tiny fly or moth that you might not notice, but the mine is a distinctive sign.

To observe leaf mines, turn over goldenrod leaves and look for translucent trails or brownish patches. A hand lens can reveal the larva inside if it is still present, or the frass (insect droppings) that often lines the mine. Leaf mines are common in late summer and fall, and the leaves may be damaged but the plant generally survives. If you find a mined leaf, you can collect it and keep it in a container to rear the adult insect, which is a rewarding project for patient observers.

Why goldenrod attracts these insects

Goldenrod is a keystone plant in late summer and fall, supporting a huge diversity of pollinators and other flower visitors, but its leaves and stems also support many herbivores. The plant produces a rich array of nutrients, and many insects have evolved to specialize on goldenrod. Goldenrod's abundance in fields, roadsides, and prairies makes it a reliable host. Additionally, goldenrod has chemical defenses, but specialists have adapted to tolerate or detoxify these compounds. This coevolution has led to a close relationship between goldenrod and its gall makers and leaf miners. When you see a goldenrod patch, you're looking at a complex community of insects, from the showy monarch butterflies feeding on nectar to the hidden larvae inside galls and mines.

Seasonal timing and what to look for

Observing galls and leaf mines on goldenrod is best done from late summer through winter. Galls are fully formed by late summer and remain visible after the plant dies back. In fall and winter, galls are easier to spot against the bare stems and snow. Leaf mines are most apparent in mid to late summer when leaves are still green, but old mines persist on dried leaves. When out for a walk, bring a hand lens, a small knife for cutting open galls (if you choose to do so), and a notebook to record your observations. Note the type of gall, its location on the plant, and the species of goldenrod if you can identify it. This attention to detail mirrors the practice of keeping field notes for birdwatching, and the same patience and observation skills apply.

On your next outing, take time to look closely at goldenrod plants. You might find the round ball gall of the goldenrod gall fly or the feathery bunch gall at the top of a stem. Check the undersides of leaves for the winding trails of leaf miners. Remember to be respectful of the habitat: avoid collecting too many galls or leaves, and be mindful that overwintering insects depend on these structures. By observing these hidden insects, you deepen your connection to the prairie ecosystem and notice the small wonders that often go unseen.