For some unknown reason, willows are extremely susceptible to gall induction and growth manipulation - in fact, Salix is one of the plant genera with the highest known numbers of associated galler species. Willow galls are induced by cecidomyiid midges, sawflies, and mites. The gall inducer can usually be identified on the basis of the willow species and the shape and location of the gall.

Gall midges (Diptera: Cecidomyiidae)

Various gall midges are diverse and common on willows, and the species can usually be identified on the basis of the shape of the induced gall. The damage caused by gall midges often seems disproportionate in relation to the size of the produced larva, which is typically less than 5 mm.

Rabdophaga rosaria

(Diptera: Cecidomyiidae)

Oviposition of this species halts the lengthwise growth of infected willow shoots. As the leaves continue to grow, a characteristic "rose" is formed at the tip of the shoot. The species occurs on many willow species, and the small red larva can be found in the center of the rosette.


"Shoot-tip rose" induced by the gall midge Rabdophaga rosaria on Salix myrsinifolia.


Rabdophaga rosaria

(Diptera: Cecidomyiidae)

Shoots galled by R. rosaria die after the summer, but the dry roses remain on the plants over the winter. In the spring, a new generation of midges emerges from pupae inside the roses.


Dry "willow roses" induced by Rabdophaga rosaria are easy to find during winter and early spring.

The pupa of the gall midge (or attacking parasitoids) can be found in the center of the rosette by cautiously removing the dry leaves.

Rabdophaga salicis

(Diptera: Cecidomyiidae)

This species induces large hollow shoot galls on many willow species. Galled shoots usually die as a result. R. salicis galls tend to be rounder and larger than the shoot galls induced by Euura sawflies.


Shoot gall induced by Rabdophaga salicis on Salix caprea.

Shoot galls induced by Rabdophaga salicis on Salix cinerea.

Rabdophaga salicis

(Diptera: Cecidomyiidae)

Midge larvae are red, small, and headless, which makes it easy to separate them from stem galls induced by Euura sawflies. Also the larval chamber is larger in the midge galls, and no frass is present.


Larva of Rabdophaga salicis inside stem gall on Salix phylicifolia.


Rabdophaga degeeri

(Diptera: Cecidomyiidae)

This midge species induces shoot galls on Salix purpurea. The galls can be very numerous on isolated S. purpurea bushes, and shoots with large galls often die.


Rabdophaga degeeri galls on Salix purpurea in the spring. The dry gall on the left is from the year before last summer, note the small exit holes on the surface.

Opened Rabdophaga degeeri gall. Each gall contains multiple midge or parasitoid larvae or pupae. The adults emerge in the spring.

Iteomyia capreae

(Diptera: Cecidomyiidae)

This species can be found on many willow species. The galls, which often occur as clusters, resemble small volcanoes on the underside of the leaf. One tiny reddish larva occupies each "volcano."


Leaf galls of Iteomyia capreae on Salix caprea.

Iteomyia capreae galls along leaf midrib on Salix glauca.

Gall-inducing sawflies (Hymenoptera: Tenthredinidae)

Sawflies that induce galls on willows belong to two different groups of the tenthredinid subfamily Nematinae. The larger of these groups is the monophyletic subtribe Euurina, which contains over 400 species that are usually divided into three main genera (Phyllocolpa, Pontania, and Euura). The species induce leaf folds or rolls, or various closed galls on willow leaves, petioles, buds, or shoots. Below are just a few examples of closed galls induced by Euurina species, click here for more pictures and information on Euurina gallers. The second, smaller sawfly galler group on willows is the genus Brachycoluma (= Decanematus), which probably includes only about 20 species. Brachycoluma sawflies induce shoot deformations that lead to the formation of a leaf bundle at the tip of a willow shoot.

Pontania glaucae (left)

(Hymenoptera: Tenthredinidae)

Species in the Pontania dolichura -group induce galls that resemble two parallel sausages next to the leaf midrib of many willow species. One larva inhabits each sausage.


Pontania polaris (right)

(Hymenoptera: Tenthredinidae)

Pontania species also induce many kinds of roundish, pea- or bean-shaped galls on willow leaves. Pontania polaris is a hardy species which occurs on the arctic-alpine dwarf willows Salix polaris and S. herbacea. P. polaris was probably one of the earliest insects to arrive in Fennoscandia after the ice retreated at the end of the Pleistocene.


Double sausage gall of Pontania glaucae on Salix glauca.

Bean gall of Pontania polaris on the dwarf willow Salix polaris.

Euura amerinae (left)

(Hymenoptera: Tenthredinidae)

Euura amerinae induces large multilarval shoot galls solely on Salix pentandra. The galls of other Euura shoot gallers are smaller and more spindle-shaped, and each of them is inhabited by a single larva.


Euura lanatae (right)

(Hymenoptera: Tenthredinidae)

Species in the Euura mucronata -group induce bud galls on many different willow species. The larvae of most species exit the galls in the autumn to pupate on the ground, in others pupation occurs inside the bud. Vacated dead buds may remain on the willow shoots for several years.


Multilarval stem gall of Euura amerinae on Salix pentandra.

Old vacated bud gall of Euura lanatae on Salix lanata. Note the exit hole on the side of the galled bud.

Brachycoluma sp.

(Hymenoptera: Tenthredinidae)

Shoot deformations caused by sawflies in the genus Brachycoluma resemble the leaf shelters constructed by many moth larvae (click here to see moth bundles). Brachycoluma bundles are technically galls, because plant growth is modified by the sawflies: while ovipositing, the sawfly females inject an unknown substance into the growing willow shoot. As a result, the leaves of the shoot become soft and sticky, and they are tightly glued together.


Shoot deformation caused by Brachycoluma sp. on Salix phylicifolia.

Brachycoluma sp. on Salix phylicifolia.

Gall-inducing mites (Acari: Eriophyidae)

Pouch galls induced by eriophyid mites (Arachnida: Acari) are common on the leaves of many willow species. Mites are not insects but arachnids, but the galls are shown here because they resemble the ones induced by insect gallers. The extremely small mites live on the hairy inner surfaces of the thin-walled pouch galls. Some eriphyid mites also cause willow leaf margins to become tighly rolled upwards.

Mite galls

(Acari: Eriophyidae)

There are probably many eriphyid mite species making pouch galls, and the identity of these two on the right is still a bit uncertain.


Eriphyid mite galls on a Salix phylicifolia leaf.

Eriophyid mite galls on Salix phylicifolia leaves.

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