Along the way, most of the new group stopped eating only bark, as most of their relatives did. They became farmers, raising mold for food in their little tree-tunnels, a bit like the way carpenter ants raise mold underground. This may have helped the beetles conquer a wide new variety of trees, said Benjamin Normark of the University of Massachusetts at Amherst, another of the researchers. That's because the mold itself can feed on a wide variety of trees, while most wood-boring insects must stick to a particular type. This means the males have just one set of chromosomes, strings of genetic code used to build an animal.
Most sexual animals have two sets, one each from the mother and father.
Having only one means no father is needed. This system isn't unique. There are 16 other types of haplodiploid animals, representing a wide variety of lifestyles and habitats, including ants and bees, Jordal said. Matings are almost always between sister and brother, or mother and son. This gives the bugs extra flexibility to colonize new areas.