Grasshoppers are common insects, often seen as pests of field crops, grasses, and garden plants. While they are known for their broad diet, they are generally not the primary threat to a mature, healthy oak tree. Grasshoppers are considered opportunistic feeders; they usually ignore the tough foliage of large trees, but certain conditions or specialized species can change this behavior.
The Typical Grasshopper Diet
Most species of grasshoppers are polyphagous, consuming a wide variety of plants, but they strongly prefer monocots like grasses and cereal crops. Their favored meals include low-lying herbaceous plants, tender seedlings, and softer leaves. They are equipped with specialized mouthparts, including robust mandibles, designed for cutting and grinding plant material. This chewing apparatus is highly effective on soft tissue but is less suited for the hard, waxy cuticle and dense cellulose of mature oak leaves. Consequently, the typical grasshopper would expend too much energy climbing and chewing an oak leaf compared to eating a blade of grass.
Conditions Leading to Oak Tree Feeding
Grasshoppers only turn to oak trees when their usual, preferred food sources become depleted or unavailable. This shift is often triggered by environmental stressors, primarily severe drought conditions. As grasses and tender annuals dry up and die, large populations migrate in search of any remaining green foliage, forcing them onto hardier plants like oak trees. Massive population outbreaks also compel them to consume nearly all available plant matter, including tree foliage. During these events, competition for food overrides their usual preferences, pushing them to climb higher into the canopy.
Specialized Species
The Post Oak Grasshopper (Dendrotettix quercus) is an exception, as it is specifically adapted to feed on oak trees. This species prefers the leaves of post oak, water oak, and blackjack oak, and can cause localized defoliation. Even this specialized species may only seek out other trees after their preferred oak hosts have been severely damaged.
Visual Signs of Grasshopper Damage
Confirming grasshopper damage involves looking for specific signs left by their chewing mouthparts. Grasshoppers create irregular, ragged holes in the leaves, often starting at the leaf edge and working inward, leaving rough edges. Unlike other common pests, grasshoppers rarely “skeletonize” leaves (associated with Japanese beetles) or cause fine, pale speckling (stippling, associated with sap-sucking insects). Feeding is usually concentrated on the lower branches and canopy, as this is the easiest part of the tree to access from the ground. Finding their brown, pelleted droppings, known as frass, on the leaves or ground beneath the tree also confirms their presence.