Are the leaves of your cherry or pear tree looking a bit ‘skeletal’? Like the green has been eaten away leaving only the brown tracery of leaf veins. If so, the culprit may be the voracious little cherry slug, which is actually not a slug but the larva of a sawfly, which is actually not a fly but a close relative of bees and wasps.

Look closely at the leaves and you may see some small, black, slimy, slug-like creatures that smell sickly sweet. So how did they get on your tree and what can you do about it?

In spring and summer the adult sawfly, Caliroa cerasi, flies to a host tree and uses a tiny saw-like organ to cut open the leaf and deposit a single egg inside the leaf where it is well protected. A week later the egg hatches and the larva starts eating and eating and eating. After 3-4 weeks of this feeding the larva drops to the ground, forms a cocoon, pupates and emerges as an adult 3-4 weeks later. The cycle then repeats.

The second-generation causes most of the damage so controlling this pest early is important. Encouraging natural predators such as paper wasps, birds and spiders will help keep this pest at bay. Other controls are available and your local garden centre is best placed to advise you on these.

The adult sawfly Caliroa cerasi is about 0.5-0.6cm in length.	Cherry ‘slug’ and typical leaf damage.