Stick insects, or walking sticks, are relatives of grasshoppers. In northern areas I've encountered small walking sticks that are two to three inches long, and their camouflage is so good that they really do blend right in with sticks and stems.
Only here in Texas have I seen the spectacular giant walking sticks that fall out of our live oak trees on occasion. These insects are four to six inches long, the females being significantly larger than the males, although some species of walking sticks can reproduce by parthenogenesis. The photo of the yellow and black striped insects mating was taken in central Florida; I've never seen this species in our area. However, it does give a good example of the size discrepancy between the sexes and the way they mate.
Although walking sticks feed on leaves, they don't do much damage to our trees because they never seem to occur in large numbers. They are just an interesting curiosity, even to our dog.