Mimicking the Appearance of Termites: Morphological Description of the Rove Beetle Austrospirachtha carrijoi

Social insects that construct elaborate nests create environments that protect their colonies and allow long-term storage of resources. Such stable and resource-rich habitats often attract other organisms seeking food or shelter. In termite nests, impostors that resemble termites are occasionally found. One example occurs in the larvae of the fly genus Rhyncomya, recorded from the Little Atlas Mountains of Morocco. These larvae possess tentacle-like abdominal projections and employ chemical signals to deceive termites into recognizing them as nestmates, thereby inducing trophallaxis from the termites.

Another such impostor inhabits termite nests in Litchfield National Park in Australia’s Northern Territory. This species, the rove beetle Austrospirachtha carrijoi (family Staphylinidae), relies on morphological disguise and behavioral imitation that allow it to live quietly within termite societies.

Lateral and dorsal views of Austrospirachtha carrijoi. The abdomen extends from right to left in the figure, showing four sternites (IV–VII); darker regions represent primary sclerotization, while lighter regions indicate secondary sclerotization（感謝Bruno Zilberman & Carlos Pires-Silva提供）

Specimens of A. carrijoi were discovered inside an eroded termite mound approximately 20 cm in diameter. Interestingly, two termite taxa were present in the same nest, belonging to the genera Australitermes and Nasutitermes. This observation suggests that the beetle may interact with more than one termite lineage rather than depending on a single host species, although whether these two termites co-inhabited the mound remains uncertain.

The body length of A. carrijoi is about 2.4 mm, with coloration ranging from light to dark brown. The hind wings are almost completely reduced, leaving only small remnants and indicating a complete loss of flight ability, which reflects strong dependence on termite nests.

The abdomen is strongly modified and bent upward, with the second abdominal segment forming a curvature that positions the abdominal apex toward the head. The third abdominal segment is transformed into an inflated ovoid region that is longer than all following segments combined.

Secondary sclerotization on sternite V extends laterally and distally, while sternite VI bears a sinuous distal margin of secondary sclerotization, and sternite VII shows a distal secondary sclerotized region with a medial acute projection.

Three pairs of pseudoappendages occur along the abdomen. The first pair arises near the pleural region of abdominal segment IV and ends in swollen tips bearing numerous short bristles. The second pair occurs on segment V and resembles the first pair but is smaller and less sclerotized. The third pair lies between segments VI and VIII and forms strongly sclerotized structures directed toward the abdominal apex.

These structures appear as raised lobes with expanded ends and short setae, and they are thought to play a role in mimicking the morphology or behavior of termites.

The head of A. carrijoi is slightly wider than long and appears roughly subquadrate. The antennae consist of eleven segments, with the terminal segment elongated and approximately as long as the preceding two combined.

The maxillary palps contain four segments: the first is short and transverse, the second elongated, the third longer than wide and narrowing basally, and the fourth reduced.

The mandibles are symmetrical, slender, and lack teeth. The prementum is extremely reduced, and the labial palps are nearly indistinguishable. These features indicate a greatly simplified mouthpart structure.

Such reduction suggests that A. carrijoi may not rely on strong chewing. Instead, it may feed on soft material or possibly obtain nourishment through trophallaxis from termites, although this idea remains speculative because no behavioral observations or gut analyses have yet been conducted.

At present, little is known about how A. carrijoi moves within termite nests, what it feeds on, or how termites tolerate its presence. Whether the termites actively accept the beetles, ignore them, or are deceived by chemical signals remains unresolved. Termite workers and soldiers typically possess limited visual capacity, so the swollen abdominal shape of the beetle may contribute to visual mimicry, but chemical communication likely also plays an important role. Further behavioral and chemical studies will be required to clarify these interactions.

Author: Shui-Ye You

Reference:

Zilberman B and Pires-Silva CM. (2023). A new species and morphological notes on the remarkable termitophilous genus Austrospirachtha Watson from Australia (Coleoptera: Staphylinidae: Aleocharinae). Zootaxa.