Norfolk is a paradoxical place. Rainfall here is low, especially in the Brecks. But we also have a lot of wet places, the most famous of which are the Norfolk Broads, where Common Reed (Phragmites australis) can form large reedbeds.

Reedbeds provide a habitat for birds such as the Bittern and Marsh Harrier, which are increasing in number, thanks to sympathetic management by organisations such as the RSPB and Norfolk Wildlife Trust. 

Less well known, reedbeds in East Anglia also support over 700 species of invertebrates, including 23 Red Data Book species. Many of these are hard to find, as reedbeds are wet places, dense and difficult to access. But if you walk beside the edge of a reed bed, or even along a thin line of reeds by a riverside path, you may find signs of one particular insect. 

Reeds grow new shoots from the base of the plant every year, each of which normally ends in a flowerhead. But if you look carefully you may find that some of the reeds are shorter than the rest. Instead of growing up into a flower head, their stems end in a cigar-shaped gall, up to a few inches long.

Cigar galls are formed by Lipara lucens, a type of Frit Fly, from the family Chloropidae. The adult flies are on the wing in June and the females lay their eggs in the stems of Common Reed. Once the egg hatches, the larva bites into the growing reed shoot. This disrupts the balance of plant hormones in the reed (indole-3-acetic acid, IAA, and abscissic acid, ABA), causing a gall to form. 

The larva feeds singly inside its gall during the summer and eventually pupates, to emerge as a new fly in the following summer.

In summer Cigar Galls are green and blend in with the surrounding reeds, but by September they become easier to spot, as they start to turn brown at the tip and the reed begins to die back. By winter the reeds and galls are both brown, and galls remain easy to spot throughout the winter and early spring, until the reeds start to produce the next year’s shoots.

Once the fly has emerged from its gall, the old Cigar Gall is sometimes used as a nest site by the Reed Yellow-face Bee, Hylaeus pectoralis. The nest can contain up to eight cells, arranged one on top of the other and sealed with leaf fragments. The female Yellow-face Bee has no pollen-collecting hairs on her legs or abdomen, but simply ingests pollen and nectar, and carries it back to her nest in her crop. The bees can also nest in hollow reed stems without galls, and in areas where Lipara lucens isn’t present.

Not every Lipara lucens larva survives to become an adult fly. Cigar Galls can provide a tasty snack for Blue Tits and Harvest Mice during the winter. The fly Cnemopogon apicalis (family Scathophagidae) eats the larva and pupates in the gall. The parasitic wasp Stenomalina liparae lays its eggs in the larva and emerges from the shrivelled corpse in spring.

To make matters even more interesting, Lipara lucens galls can also be used as a home by a number of other insect lodgers, known as inquilines (from Latin inquilinus, “lodger” or “tenant”). 

Life in the insect world is always fascinating.

Further Reading

The Plant Parasites of Europe website has pictures of the Cigar Gall and the developing Lipara lucens fly, as well as a list of inquilines.

Dr. Tom Reader, from the University of Nottingham, has written a fascinating piece about Lipara.

Buglife have produced a list of Notable invertebrates associated with reedbeds.