Many beetle larvae and some adults burrow and are rarely seen unless one purposefully goes looking for them. But these beetles do not just burrow underground. Some are found in punky wood, bore into trees, burrow beneath the bark of trees, bore into the stems of herbs, or produce galls.
Ground Dwellers
Ground dwelling beetle larvae and adults may be carnivorous or herbivorous. Carnivores such as found in the family Carabidae may be monochromatic like the black or brown ground beetles that often burrow as both larvae and adults and can be found beneath logs and rocks. These feed on many species of injurious pests and should be returned to the soil without injury when found. The carnivorous larvae of the often brightly colored caterpillar hunters feed below ground, while the adults comb foliage after dark searching for caterpillars and many pest insects.
The herbivorous beetles, such as the wireworms of click beetles and grubs of scarabs, are among the most destructive of crop pests. They live in the soil where they eat seeds, cut off roots and stems, and bore holes in larger stems, roots, and tubers. Adult click beetles also feed on plant materials, but are less destructive than the larvae.
Most plant damaging soil grubs are larvae of beetles in the scarab family that were introduced from Asia and Europe: Japanese beetles (Popillia japonica), Oriental beetles (Exomala orientalis), Asian garden beetles (maladera castanea), and European chafers (Rhizotrogus majalis). While their larvae eat plant and grass roots – sometimes producing bald spots in otherwise well manicured lawns, the adults eat pollen, nectar, leaves, and stems – often becoming pests as they damage flowers and defoliate entire plants.
Punky Wood Feeders
Stag and bess beetles (Odontotaenius disjunctus) lay their eggs in punky wood of logs or stumps. Their larvae are grub-like and take several years to grow to full size which could be as long as two and a half inches and a half inch in diameter. After pupating over their last winter, the adults emerge in spring or summer, mate, and reproduce. Adults often feed on plant saps and fruits.
Tree Borers
The long-horned beetles of the family Cerambicidae produce flattened grubs that bore through live or dead trees, eating the wood, and riddling it with their tunnels. There are many native wood-boring beetles, but the recently introduced Asian long-horned beetle (Anoplophora glabripennis) is extremely destructive, attacking and killing trees in residential neighborhoods as well as forests. The US Department of Agriculture has established quarantines on transporting wood in several US cities. Wood cut in these areas must be shredded and burned in hopes of restricting the spread of these beetle through our forests.
Bark Borers
Many beetle species bore beneath the bark of trees leaving tunnels filled with frass (their feces). Elm bark beetles (Scolytus multistriatus and Hylurgopinus rufipes) burrow in elm trees and spread the fungi (Ophiostoma ulmi and Ophiostoma novo-ulmi) that cause Dutch elm disease. Southern pines are attacked by at least six species of bark beetles that damage the phloem of the plant and also transmit a blue wood fungus that destroys the crown of the trees.
The chestnut blight that reached this country in the early years of the 20th century was not spread by beetles as the spores of the chestnut blight fungus (Cryphonectria parasitica) are able to penetrate the rather thin bark of upper branches and move through the entire tree. Except for a few isolated locations in the Pacific northwest, this fungus is responsible for destroying one quarter of the trees that once grew in the forests of the United States.
Stem Borers and Gall Makers
Larvae of most tumbling flower beetles in the family Mordellidae bore into stems and eat the pith and other larvae they may encounter. Most gall making beetles are of little importance in the world. Some of the Mordellidae and beetles of a few related families make galls, and those that do produce galls are not seriously injurious to their host plants. Some of these beetle larvae are in turn parasitized by wasp larvae that help control gall makers and stem borers.
Below ground as above it, insects play out their ecological roles with the same needs, food choices, predators, and parasites. They are just hidden from the casual observer. There's a whole world out there and we often overlook most of it.
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