NEW TO BRITAIN
Insects new to the Commons,or new to the Tunbridge Wellsarea, are found quitefrequently. Species new to Britainare much more unusual. In June2007, local naturalist Keith Palmerfound some unfamiliar leaf-mineson small-leaved lime on TunbridgeWells Common. These wereidentified, and confirmed byspecialists, as belonging to the larvaeof a small shiny black sawfly – calledParna apicalis - which had notbeen recorded from Britain before.
Sawflies are a group of insectswhich, although large in number(there are over four hundred Britishspecies), are little known to thegeneral public - except perhaps for
gardeners who may encounter'pest' species like the Rose,Gooseberry or Apple Sawfly. Theyget their family name from thefemale's serrated egg-laying organ,which it uses to cut slits in planttissues in order to conceal its eggs.Sawflies are related to bees andwasps, and they vary greatly in size.Some, like the Birch Sawfly with itsfast andbuzzing flight, are the sizeof a large bee, while others are smalland inconspicuous. They alsoshow a great variety of colours andpatterns. Some have yellow andblack stripes and closely resemblesolitary wasps; some are patternedin red, orange or green; while others,
like our new discovery, are plainglossy black.
Adult sawflies fly by day, and manyspecies can be found on theCommons visiting flowers or sittingopenly on sunlit foliage. Some ofthe banded wasp-like species arepredators, catching other insectswhile they are preoccupied withfeeding at flowers. The large flowerheads of umbellifers like Hogweedand Cow Parsley are especiallypopular hunting grounds becauseof the number and variety of nectarfeedinginsects they attract.
The larvae of sawflies are in somecases more conspicuous than theadults. They closely resemble thecaterpillars of moths and butterflies,having a series of additional legs or
'claspers' along the length of theirbody, in addition to the six regularjointed legs that all insects share. They are all plant feeders, and themajority feed openly on the leavesof various trees and other floweringplants and ferns. As with mothand butterfly caterpillars, thedifferent species all have their ownfavoured foodplants. Some rely oncamouflage to protect them frompredators, but others exhibitwarning colouration, seeking topersuade predators that they aredistasteful. Readers may have seenthe green and orange sawfly larvaethat feed in large groups on sallowleaves and raise the hind part oftheir bodies in unison when theyare disturbed.
Some sawfly larvae live in galls,those curious swellings that plantsproduce in response to the eggsthat particular insects inject intotheir tissues. Insects that producegalls specialise in a particular plantspecies or group of species, and theegg-laying process somehowprogrammes the plant to producea distinctive type of gall that
provides food and shelter for theinsect's young. The most wellknowninsects of this kind are thegall-wasps that produce oakapples,robin's pincushions and many otherconspicuous types.Galls produced by sawflies are fewerin number, but include the familiarpurplish swellings on willow leavesthat can be seen, for example, onthe trees along MountEphraimnear St Helena Cottage.
Other sawfly larvae, like the newlydiscovered species, are leaf-miners.Insects of several different groupshave adopted this lifestyle, whichinvolves eating away the juicy innerparts of leaves while leaving theprotective outer layers intact. Someinsects wander around inside theleaf, leaving a winding transparenttrail as they go: a good example,produced by a small mothcaterpillar, can regularly be seen onbramble leaves. In the case of ournew lime-feeding sawfly, the larvaeats away a solid area at the edge ofa leaf, leaving a translucent blotch.
Ian Beavis