Symphyta or saw flies are a sub-order of the order Hymenoptera. The main difference between saw flies and the other Hymenoptera is that saw fly adults do not have a "wasp waist", see left. Also none of them are social. There are around 6000 species of saw fly in he world, although there are no native saw flies in New Zealand.

The adults feed mainly on pollen, although some adults are partly carnivorous.

When disturbed they hold on to the leaf with their front legs and wave their rear ends in the air. Pupation takes place in a cocoon.

On the left is a drawing of a saw fly saw used in cutting into plants. Most saw flies have such structures, but some species have a more conventional ovipositor that sticks out of the rear and looks more like a drill than a saw. These are often given the name of horntails or wood wasps.

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On the right and below left is the wood wasp or horntail Urocercus gigas. It is not a wasp at all as it can be clearly seen below that it has no "wasp waist" that all bees, wasps and ants have.

Also although this female - and it is usually just the female wood wasps we see - looks fearsome, she is quite harmless. The very worst she can do is fly into you. This is a typical example of a harmless insect gaining protection from predators by mimicking a harmful one. The long, dark brown thing sticking out of her rear end is not a sting, but her ovipositor. With it she drills vertically 5 - 10 mm into wood - usually a diseased, unhealthy or dead conifer - and injects 4 - 8 eggs.