Detailed morphological and dimensional analysis of the detritus deposited in the galleries of woodboring insects was performed for some of the most common xylophagous insect larvae in timber construction in Spain. The samples studied belong to six species of four common families of borers:Cerambycidae, Anobiidae, Curculionidae and Lyctidae. The samples were provided by Spanish and German companies and laboratories. The detritus was assessed for size, shape, and colour and, for different species, was found to show morphological and dimensional differences, enabling betterand faster identification of these destructive agents. Frass shape and colour assessment together with statistical dimensional data of the six species are presented. A predictive function based on length and width variables of the detritus is proposed, using multivariate discriminant analysis methodology. This function has been proven to be more than 78% effective in tests of the model.