Formosan Termites in Southern California — What You Need to Know

What Are Formosan Termites?

Formosan termites (*Coptotermes formosanus*) are an invasive subterranean termite species originally from China and Taiwan, introduced to the continental United States through international shipping activity after World War II. They are now established in at least 11 US states, including California.

Unlike Western subterranean termites — already the most destructive native species — Formosan termites form significantly larger colonies, forage more aggressively, and can attack a wider variety of materials. They are sometimes called "super termites" because of their capacity for rapid, severe structural damage.

How Formosan Termites Differ From Other Species

Colony Size

A mature Western subterranean termite colony typically contains 200,000 to 1 million workers. A mature Formosan colony can contain 1–2 million workers or more. The difference in feeding pressure is enormous.

Foraging Range

Formosan termites forage up to 300 feet from the main colony — far beyond the typical 150-foot range of native species. This means even homes without direct soil-to-wood contact can be vulnerable if a colony is established in a nearby tree, utility pole, or neighboring structure.

Carton Nests

One of the most distinctive features of Formosan termites is their ability to build secondary "carton" nests above ground — inside walls, in attic framing, or within living trees. These nests are made from chewed wood, soil, and termite saliva, and allow the colony to retain moisture and continue feeding far from soil contact. This makes above-ground infestations significantly harder to control than standard subterranean infestations.

Feeding Rate

Formosan termites can consume approximately 13 ounces of wood per day — compared to about 7 ounces for a similarly-sized Western subterranean colony. In practical terms, this means structural damage that would take native termites years can occur in months with an established Formosan colony.

Signs of Formosan Termite Infestation

The signs of Formosan termite activity overlap with other subterranean species, but a few indicators are more specific:

• Night swarming in May–July: Formosan swarmers are attracted to light and swarm after dark — typically on warm, humid evenings between May and July. If you see large numbers of swarmers at night around your outdoor lights during this window, Formosan termites are a real possibility.
• Yellowish-brown swarmers: Formosan swarmers are slightly larger than Western subterranean swarmers and have a yellowish-brown body with pale wings covered in small hairs.
• Carton material in walls: During repairs or renovations, if you discover a grayish, paste-like material inside walls or framing that doesn't match the surrounding wood or insulation, this may be a Formosan carton nest.
• Mud tubes: Like all subterranean termites, Formosans build mud tubes to travel above ground. Their tubes tend to be broader and more irregular than those of native species.
• Accelerated visible damage: If structural wood seems to be deteriorating faster than expected — floors buckling, walls showing settlement cracks, door frames warping — and moisture isn't the cause, an aggressive subterranean infestation like Formosan should be considered.

Are Formosan Termites Common in Orange County and Southern California?

Formosan termites are less common in Southern California than in the Gulf Coast states (Louisiana, Florida, and Hawaii have the heaviest infestations), but established populations exist in the state. California's ports — particularly Long Beach and Los Angeles — have historically been entry points for invasive species. Urban trees, especially the old-growth trees common in older neighborhoods of Orange County, Long Beach, and LA, can harbor established colonies.

The California Department of Food and Agriculture and the University of California Cooperative Extension have documented Formosan termite activity in several Southern California counties. The risk is real, particularly in older neighborhoods with mature trees.

Treatment for Formosan Termites

Because Formosan colonies are larger and can form secondary above-ground nests, treatment is more complex than for native subterranean species.

Liquid Barrier (Termidor) — The most effective treatment for subterranean Formosan termites. Termidor (fipronil) is applied as a continuous treated zone in the soil around the foundation. Because termites transfer the product to nestmates through normal social contact (the "transfer effect"), entire colonies can be eliminated even when workers carry the product back to inaccessible nesting sites.

Borate Treatment — Tim-bor or Boracare applied to structural wood provides long-lasting protection against any termite species that attempts to feed on treated wood. Often used in conjunction with soil treatment for comprehensive protection.

Tent Fumigation — If above-ground carton nests are present inside the structure, fumigation may be the most reliable option. Vikane gas penetrates all wood members and kills all termite life stages, including those in inaccessible carton nest locations.

Baiting systems (e.g., Sentricon) can reduce Formosan colony populations but are generally considered slower-acting against Formosan than against native subterranean species, due to colony size and behavioral differences.

When to Call a Professional

If you see night-swarming insects near outdoor lights in late spring or early summer, or if you notice any of the infestation signs described above, schedule an inspection promptly. Correctly identifying the species matters — the right treatment for a Formosan infestation differs from a standard drywood termite recommendation.

Our licensed inspectors serve Orange County, LA County, the Inland Empire, and Riverside County. Schedule a free inspection or call (714) 240-2800.

Related: Subterranean Termite Guide · Liquid Barrier Treatment (Termidor) · Termite Inspection