Dull and damp.
Two versions of the mine of the Agromyzid fly Phytomyza angelicastri on Angelica. It can be seen that the mine shape depends entirely on where the egg is laid and in which direction the larva starts to burrow. Some species are very particular about where they lay their egg, and their mines are very predictable in shape. Other species (like this one) lay almost anywhere on the leaf and the mine takes shape according to which boundaries or obstructions the larva encounters. It follows, therefore, that mine shape can only be used to determine species in a subset of the mines encountered.
