What is the large beetle I found near my palo verde tree?

It is likely the Palo Verde Longhorn Beetle (Derobrachus geminatus) — one of the largest beetles in North America at up to 3.5 inches. Adults are gray-brown, emerge in June–August, and are attracted to lights. They do not bite.

What are the round holes in my tree trunk?

Round to oval holes (1/4 to 1/2 inch diameter) in bark are emergence holes where adult longhorn beetles chewed out after pupating. This is a sign of a completed infestation — larvae have already caused damage inside.

Can longhorn beetles kill my Arizona trees?

Yes — severe infestations can kill trees, especially stressed ones. Healthy, well-watered trees are much more resistant. Drought-stressed, recently transplanted, or injured trees are most vulnerable.

How do I protect my trees from longhorn beetles?

Maintain tree health with deep, regular watering. Avoid soil compaction and physical injury. For high-value trees, apply permethrin or bifenthrin to bark in May–June before adult emergence.

When are longhorn beetles active in Arizona?

Adults emerge in summer (June–August) and are attracted to lights at night. Larvae are active inside wood year-round for 1–3 years before emerging as adults.

Is the Palo Verde Longhorn dangerous?

No. Despite its large size and intimidating appearance, the Palo Verde Longhorn does not bite and is not aggressive. It is a native species and part of the desert ecosystem.

What trees do longhorn beetles attack in Arizona?

Palo verde, mesquite, and desert legumes (Palo Verde Longhorn). Pine trees at higher elevations (Roundheaded Pine Borer). Cottonwood and willow along waterways (Cottonwood Borer). Oak, sycamore, and ornamentals (various species).

Should I remove a tree with longhorn beetle damage?

Not necessarily. A healthy tree can tolerate some damage. Severely infested, declining trees may need removal. Consult an arborist to assess the extent of damage and tree health before deciding.

Bugs & Beetles

Longhorn Beetles in Arizona: Wood-Boring Damage, Identification & Control

Back to Blog9 min readArizona

Longhorn beetles are a diverse group of wood-boring insects found throughout Arizona, from the iconic Palo Verde Longhorn to species that attack pine, oak, and ornamental trees. Their larvae bore deep into wood, causing structural damage and tree death. Learn how to identify longhorn beetle damage, protect your trees, and know when professional treatment is needed.

Longhorn beetles (Family Cerambycidae) are one of the most diverse beetle families in North America, with over 1,000 species in the United States. In Arizona, they range from the spectacular Palo Verde Longhorn (Derobrachus geminatus) — one of the largest beetles in North America at up to 3.5 inches — to smaller species that attack pine, oak, sycamore, and ornamental trees. The name comes from their most distinctive feature: antennae that are often as long as or longer than the body. All longhorn beetles share the same basic life cycle: adults emerge in summer, mate, and lay eggs in bark crevices or on the surface of stressed or dying trees. Larvae bore into the wood, feeding on the cambium layer and heartwood for 1–3 years before pupating and emerging as adults. This wood-boring activity is what makes them economically significant. The Palo Verde Longhorn is the most commonly encountered species in Arizona's urban and suburban landscapes. Adults are large, gray-brown beetles that emerge in June–August, attracted to lights at night. They are alarming in appearance but do not bite and are not aggressive. Their larvae feed on the roots and lower trunk of palo verde trees, mesquite, and other desert legumes. A healthy tree can tolerate some larval feeding, but stressed trees (drought-stressed, recently transplanted, or damaged) can be killed. The Roundheaded Pine Borer (Ergates spiculatus) attacks pine trees in Arizona's higher elevations. The Cottonwood Borer (Plectrodera scalator) — a striking black and white beetle — attacks cottonwood and willow trees along Arizona waterways.

Common Arizona Longhorn Beetle Species

Species	Size	Host Trees	Season
Palo Verde Longhorn Derobrachus geminatus	Up to 3.5 inches	Palo verde, mesquite, desert legumes	Jun–Aug
Cottonwood Borer Plectrodera scalator	1–1.5 inches	Cottonwood, willow	Jun–Aug
Roundheaded Pine Borer Ergates spiculatus	1.5–2.5 inches	Pine (higher elevations)	Jul–Sep
Mesquite Borer Placosternus difficilis	1–1.5 inches	Mesquite, acacia	Jun–Aug

Identifying longhorn beetle damage requires knowing what to look for. The most diagnostic sign is the emergence hole: a round to oval hole, 1/4 to 1/2 inch in diameter, in the bark of the trunk or branches. This is where the adult beetle chewed its way out after pupating. You may also see sawdust-like frass (wood shavings mixed with feces) at the base of the tree or packed into bark crevices. On the bark surface, look for egg-laying scars — small, crescent-shaped cuts in the bark where females have deposited eggs. Under the bark, the larval galleries are distinctive: winding, packed-with-frass tunnels that cut through the cambium layer and disrupt the tree's vascular system. Trees with extensive gallery systems show symptoms of decline: yellowing leaves, branch dieback, reduced growth, and eventually death. In Arizona, longhorn beetle attacks are strongly associated with tree stress. Drought-stressed trees, recently transplanted trees, trees with root damage, and trees with physical injuries are far more susceptible than healthy, well-watered trees. This is why longhorn beetle damage often appears after periods of drought or following construction activity near tree roots. Monitoring for adult beetles in summer (June–August) and inspecting trees for emergence holes and frass in late summer and fall provides early warning of infestations.

Stressed Trees Are Most Vulnerable

Drought-stressed, recently transplanted, or physically injured trees are far more susceptible to longhorn beetle attack. Maintaining tree health is the most important prevention strategy.

Protection & Treatment

Longhorn beetle management focuses on tree health and prevention, with chemical treatment playing a supporting role. The most important strategy is maintaining tree health: water trees deeply and regularly during drought periods, avoid soil compaction around root zones, and protect trees from physical injury. Healthy trees produce defensive compounds (resins, tannins) that deter egg-laying and kill young larvae. For high-value trees in areas with known longhorn beetle pressure, preventive insecticide applications can be effective. Permethrin or bifenthrin applied to the bark of the trunk and major branches in late spring (May–June) before adult emergence creates a residual barrier that kills adults before they can lay eggs. Systemic insecticides (imidacloprid soil drench) can protect trees from some longhorn species but are less effective against species that primarily attack the root zone. For trees with active infestations, the options are limited once larvae are established inside the wood. Injection of insecticide directly into larval galleries (using a syringe) can kill individual larvae but is impractical for large infestations. Biological controls — parasitic wasps and nematodes — are used in commercial forestry but are not widely available for homeowner use. For severely infested trees that are declining, removal and replacement with a resistant species is often the most practical solution. Dispose of infested wood promptly — do not store it near healthy trees, as adults can emerge from cut wood and attack nearby trees.