Psyllids or Jumping Plant Lice are small, jumping, winged, highly host-specific plant-feeding bugs in the Superfamily Psylloidea. Not only can Psyllids weaken plants with their feeding and spread plant diseases, their nymphs (immature Psyllids) can form unsightly, disfiguring galls on host plants. I observed these weird, red, pimple-like galls on the leaves of an 'Ohi'a Lehua (Metrosideros polymorpha), a native Hawaiian flowering tree.

The cone-shaped galls are those of an Ohia Psyllid (Trioza sp.), and they are typically found on the tender young leaves of 'Ohi'a Lehua trees. Adult female Psyllids lay their eggs halfway inside the leaves of their host plant, and the hatched young then enter the leaves to feed on them. As they feed, the nymphs secrete substances that stimulate abnormal plant growth, forming galls over the feeding nymphs.

The nymphs remain in their protective galls until they are ready to emerge and molt into mature, winged adults. Although the strange-looking galls are quite conspicuous, the small, adult Psyllids are inconspicuous and not often observed.