California timema (Timema californicum) in the Santa Cruz Mountains. Timemas are a type of walking stick found mainly in California but also parts of Nevada, Arizona, Oregon, and Northern Mexico. They form a very ancient lineage of stick insects (order Phasmatodea) and thus have many characteristics that differ from the rest of the order. However, like all other phasmids, they are herbivores and rely on their camouflage to evade predation. After mating, the male will ride on the female's back and "guard" her for up to 5 days. This is what's going on in the first picture. Several timema species (but not this one) are parthenogenetic, meaning they only reproduce asexually and are almost entirely female (some species do rarely produce males and no one knows why). Two species have not reproduced sexually for over 1 million years, the longest of any insect!
