Galls caused by sawflies

All images on this website have been taken in Leicestershire and Rutland by NatureSpot members. We welcome new contributions - just register and use the Submit Records form to post your photos. Click on any image below to visit the species page. The RED / AMBER / GREEN dots indicate how easy it is to identify the species - see our Identification Difficulty page for more information. A coloured rating followed by an exclamation mark denotes that different ID difficulties apply to either males and females or to the larvae - see the species page for more detail.

Galls

The British Plant Gall Society define a gall as ‘an abnormal growth produced by a plant or other host under the influence of another organism. It involves enlargement and/or proliferation of host cells, and provides both shelter and food or nutrients for the invading organism'. (https://www.britishplantgallsociety.org/)

Organisms that cause galls to form on plants encompass almost the entire spectrum of life – from viruses and bacteria, through Protozoa, fungi and allies, slime-moulds, nematodes, mites, aphids and psyllids, flies, beetles, moths, sawflies and wasps, and even a few algae and vascular plants.    The organism that causes a gall is usually very difficult to identify, but often the gall can be identified.   However, some galls are hard or impossible to identify, and it may be necessary to find the gall-causer and get expert help.  The presence of parasitoids, inquilines or other organisms sheltering or feeding inside an occupied or vacated gall can be misleading, and it is common to find atypical specimens or chimaera formed by two or more organisms in close proximity - usually these can't be identified.  

When recording galls, always start by identifying the host plant accurately and make sure you have included information on the host in the notes attached to your record.  Most species of galls are specific to a host, and this is always the first step in identification.

The Field Studies' Council's  AIDGAP guide by Redfern, M. & Shirley, P. (2023) ‘British Plant Galls’ (3rd edition). FSC is recommended.

The BPGS Facebook group can help with identifying galls: British Plant Galls. 

Photos can be found on the BPGS website or on these northern European websites:

In the accounts below, there are sometimes two or more Red-Amber-Green or 'RAG' ratings - one or two referring the gall, and one to the gall-causer.  Galls usually have a lower 'RAG' rating then the causer.  Click on the species to find out more. 

Galls caused by sawflies

Unlike other insects, it is the ovipositing female that initiates the galls, rather than the larva.   Gall-forming is not common in sawflies, and nearly all belong to the family Tenthredinidae, sub-family Nematinae, and gall Salix species (willow and sallows).  One species causes an open gall on Blackthorn, and another in the sub-family Blennocampinae causes a leaf roll on wild Roses. 

Each Salix species trends to have its own sawfly gall-causer, and so it is essential for he host plant to be accurately identified.  Unfortunately, Salix are not easy to identify; some guidance is in NatureSpot's Trees and Shrubs species galleries.  Sawfly taxonomy is also subject to change, and synonyms are common.  

The familiar bean galls in willows and sallows are often recorded.  Sawflies also cause stem galls, simple swellings that are often overlooked and rarely recorded, open leaf-folds (Phyllocolpa species) and bud galls.  These are all difficult to identify with certainty.