Sawflies Talk by Andrew Halstead, 11 January 2006

Ross and I had been wondering about the identity of the small 'caterpillars' that managed to strip one of our Berberis bushes completely bare last summer.  All was revealed by Andrew Halstead, Principal Entomologist at Wisley RHS Garden, during his fascinating talk earlier this year - they were sawfly larvae.

Sawflies belong to the same order as the wasps, ants and bees - the Hymenoptera - and indeed the adults look rather wasp-like, but unlike wasps they have no constriction between the thorax and abdomen.  They have no sting, but the female of most species has a saw-like appendage at the end of the abdomen which is used to cut holes into plants into which eggs are laid: hence the name.  The larvae of most species, unlike the grub-like larvae of wasps, ants and bees, have a well developed head and legs, and look very like Lepidopteran caterpillars.  However, sawfly larvae have at least six pairs of abdominal pro-legs, whereas caterpillars have a maximum of five. (For those with Web access there are some rather nice photos at http://www.kean.edu/~symphytos/ - although these are largely North American species.) The larvae of many species are gregarious, feeding in a cluster.  Sawflies pupate in a coccoon of silk, in the soil or leaf litter, or attached to the food plant.

While the adult sawflies may be carnivorous, the larvae are plant-eaters, ranging from leaf grazers to leaf miners, and some are even gall causers.  The bean gall sawfly, for example, produces a bean-like swelling on willow.  Some species cause leaf-curling, the result of a chemical injected by the female during egg-laying.  Although most species do not cause serious damage to their hosts, a number do, and some are considered pests.  Examples include gooseberry sawfly (three species), iris sawfly, which can affect cultivated Iris, turnip sawfly, large rose sawfly (two species) and apple sawfly.  A relatively recent addition to the British list - made by Andrew himself - is Arge berberidis, which as the name suggests lives on certain Berberis species (and was the beast that ate our plant!) as well as Mahonia.

There are several families of sawflies, including the Diprionidae, which are mainly conifer feeders, and the Cephidae, whose larvae are stem borers, living on grasses, sedges and rushes.  The Siricidae, commonly known as 'wood wasps', as the name suggests feed on woody species, and instead of a saw-like ovipositor the females have a fearsome-looking needle-like ovipositor capable of drilling into wood.   However, the vast majority of sawfly species - some 420 - belong to the family Tenthredinidae.

There is still much to be learned about most of these species, and indeed about how many are resident here, so keep your eyes open for these tiny but fascinating creatures this summer.

LYNN WHITFIELD