It has 4 white rust-tipped tussocks along its back. There are two pencil like tufts of black spines that point frontwards from the thorax and a single tuft of black spines that points posteriorly from the end of the abdomen. The long fine hairs protect the larva from predation from other insects such as ants. A close up view of the tussocks shows also the strong white spines that surround the red lateral spots along the body. More about these later.
All caterpillars have special prolegs on the abdomen that are used to grip the branch or needles.
Here you see a view of the 4 pairs of prolegs on the underside of a DFTM caterpillar. The prolegs have chitinous hooks or crotchets that help to grip smooth surfaces. When the caterpillar is fully fed, it is ready to begin the transition to the adult stage. The caterpillar lays down a layer of silk and then begins to weave a cocoon over itself. As the larva turns inside this cocoon, its spines stick through the silk and snap off.