The Hawaiian happy face spider Theridion grallator (Theridiidae) exhibits a spectacular array of color morphs, which can be plain either ‘yellow’ or ‘patterned’ (red, black or white patches differing in form and extent, on the yellow background). In Maui populations abdominal color is controlled by simple Mendelian alleles, with ‘yellow’ morphs recessive to all patterned morphs. The progeny always segregate for the parental color alleles in Mendelian ratios. Fundamental differences exist in the genetics underlying color polymorphism in different populations. For example, the polymorphism appears to be controlled at a single major locus on Maui, two on Hawaii; and there is no evidence of associations of any morphs with a particular sex on Maui, whereas on Hawaii island, 4 morphs are limited to a single sex. We are investigating the mechanisms whereby these differences have arisen during colonization of the different islands. Selection appears to be operating to maintain similar frequencies of color alleles in different populations. Hawaiian bird predators are the most likely selective agent capable of modifying their feeding effort according to the frequency of a morph. This work has been conducted in collaboration is Geoff Oxford, York University, England.