2.2 Drywood Termites: Biology, Castes & Field Evidence

2.2 Drywood Termites: Biology, Castes & Field Evidence

Why This Matters

The western drywood termite (Incisitermes minor) is California's second most economically important termite after the subterranean termite, and it behaves fundamentally differently: it needs no soil, no leak, and no decay to survive, because it lives entirely inside the sound, dry wood it consumes. That independence from moisture means drywood termites can infest eaves, attic framing, window and door frames, wall studs, and furniture anywhere in a structure, including locations a subterranean colony could never reach. Because drywood infestations often require whole-structure fumigation (a Branch 1 activity) once they are widespread, a Branch 3 inspector's correct identification and clear documentation of drywood evidence directly determines what treatment recommendation follows.

Colony Structure and Biology

Drywood termites belong to the family Kalotermitidae, a lineage that, unlike the subterranean termite's Rhinotermitidae, has no true, permanently sterile worker caste. Instead, the tasks of feeding, tunneling, and grooming are carried out by pseudergates, sometimes called false workers — immature nymphs that delay their own development to perform colony labor while retaining the ability to later molt into a soldier or a winged reproductive. A drywood colony is small, typically fewer than 1,000 individuals at maturity, and takes years to build up to that size. Critically, the colony's nest and its food source are the same piece of wood: a single mated pair that swarms into a crack or exposed end grain begins a self-contained colony that never needs to forage outside the timber it occupies. As a result, a single structure can harbor many separate, unconnected drywood colonies scattered across different wood members, unlike the single expansive network typical of a subterranean colony.

Castes: Pseudergates, Soldiers, and Swarmers

• Pseudergates (false workers) are pale, translucent white to cream, soft-bodied nymphs that resemble small, wingless termites. They perform all colony labor but are not a permanent caste — any individual can still develop into a soldier or a reproductive.
• Soldiers have a large, reddish-brown to orange-brown head with two prominent teeth visible on the left mandible, a pale cream body, and measure roughly 8 to 12 mm long. The head and jaws are used to plug gallery entrances and block intruders, particularly other termite species and ants.
• Swarmers (alates) have a dark brown body with an orange-brown head and pronotum, and two pairs of dark, smoky-black wings — noticeably darker than the brownish-gray wings of a subterranean swarmer. The body measures roughly 1/2 inch (11 to 12.5 mm) long, similar in overall size to a subterranean swarmer but visibly darker-winged under a hand lens.

Caste Comparison Table

Moisture Requirements

Unlike subterranean and dampwood termites, drywood termites do not require soil contact or elevated wood moisture. They meet their water needs metabolically and from the ambient humidity already present in sound wood, which is precisely why they can colonize dry, undecayed structural members that no other termite type can reach — attic rafters, fascia boards, window sashes, and furniture with no moisture problem whatsoever. This independence from an external moisture source is the defining biological trait examiners test, because it explains why moisture-correction measures effective against subterranean or dampwood termites do nothing to stop an active drywood infestation.

Field Evidence

The diagnostic sign of drywood termite activity is the fecal pellet: a hard, six-sided (hexagonal) pellet with distinct longitudinal ridges, ranging in color from light tan to nearly black depending on the wood the colony has consumed. As galleries fill with these pellets, the colony bores a tiny kick-out hole, typically less than 2 mm across, through the wood or drywall surface and pushes accumulated pellets out like a garbage chute, leaving a small, cone-shaped pile beneath the hole on a windowsill, attic floor, or garage shelf. Because the colony never contacts soil, there are no mud tubes; galleries themselves are clean, dry, and free of soil packing, running with and across the wood grain and interconnected by pellet-lined chambers rather than the mud-streaked tunnels of a subterranean infestation.

Swarm Season and Behavior

Western drywood termite swarmers typically emerge during daytime hours in late summer and fall, commonly correlating with hot, dry conditions and, in Southern California, Santa Ana wind events. Homeowners most often first notice a colony when swarmers appear at windows or light fixtures, or when they discover a pellet pile that has accumulated beneath an unnoticed kick-out hole.

Distinguishing Drywood Termites from Other WDOs

Three traits separate drywood termites from the other pests covered in this chapter and the next: hexagonal, ridged fecal pellets (subterranean termites leave mud-packed galleries, and dampwood termites leave smooth, ridge-free pellets); complete independence from soil or added moisture (the opposite of both other termite types); and a pseudergate-based caste system rather than a permanent worker caste. Wood-boring beetles, covered fully in Chapter 3, leave powdery frass and round or oval exit holes rather than pellets and kick-out holes, which is another quick field differentiator when termite evidence is absent.

Exam Traps

• Pellet Shape Trap: Hexagonal pellets with visible ridges mean drywood termites; smooth, football-shaped pellets without ridges mean dampwood termites. Do not confuse the two.
• Soil-Contact Trap: Drywood termites need no soil contact and can infest wood with zero moisture problems, the opposite of the subterranean termite's dependency covered in Section 2.1.
• Worker Caste Trap: Drywood colonies use pseudergates (false workers), never a permanent sterile worker caste; only subterranean termites have true workers.

Field Inspection Scenario

During an attic inspection, a technician finds a small, cone-shaped pile of hard, six-sided pellets on the insulation directly beneath a pinhole-sized opening in a rafter. There are no mud tubes anywhere in the attic, no roof leaks, and the wood itself is sound and dry. This combination — hexagonal pellets, a kick-out hole, and dry, undamaged wood with no moisture source — confirms an active western drywood termite colony rather than subterranean or dampwood activity.