Cerotainia macrocera

Distinguished from the unrelated genus Eudioctria (subfamily Stenopogoninae), which is similar in size and general appearance, by its extra-long antennae. Eudioctria species have shorter antennae and prefer perching on flat leaves at the top of small shrubs, whereas Cerotainia macrocera tends to perch on twig ends. The yellowish face coloration also aids identification. The small size and long antennae separate it from larger Laphriinae such as Andrenosoma and Laphria.

A minute robber fly with body length of 6–8 mm. The most distinctive feature is the elongated antennae, which are notably longer than those of most similarly sized robber flies. The face is yellowish, giving rise to the common name. The body is slender and compact, with relatively long legs compared to body size. The mystax (facial bristles) is present but not prominently developed.

Occupies open, sunny habitats with scattered woody vegetation. Frequently found in areas with dead or dying trees that support wood-boring beetles, as these provide larval food resources. Observed in pine-oak forests, sandstone barrens, and similar dry, open woodland environments.

Eastern North America. Documented from the eastern United States, with records from Missouri, Arkansas, and surrounding regions. The genus Cerotainia reaches its greatest diversity in the Neotropics, but C. macrocera is one of the few species occurring in eastern North America.

Adults active in spring and early summer. Observations from May suggest peak activity during this period, though precise seasonal limits are not well documented.

Adults are predatory, capturing small flying insects. The specific prey spectrum has not been documented for this species. Larvae, like all Laphriinae, prey on wood-boring beetle larvae in dead wood.

Complete metamorphosis with egg, larva, pupa, and adult stages. Larvae develop in dead wood, feeding on wood-boring beetle larvae (families Buprestidae and Cerambycidae). Pupation occurs within the wood, with the pupal case sometimes protruding from the emergence hole.

Perches on twig ends and other elevated, exposed sites from which to ambush prey. Unlike the related Eudioctria, which prefers flat leaf surfaces, this species selects narrow perches. Adults are likely territorial and exhibit typical robber fly sit-and-wait predatory behavior.

Adults function as generalist predators of small flying insects. Larvae serve as specialist predators of wood-boring beetle larvae, potentially helping regulate populations of these beetles in forest ecosystems. The species contributes to nutrient cycling in dead wood habitats.

No direct economic or medical significance. Of interest to entomologists studying robber fly diversity and biology. The species is small enough to escape general notice, though it may be encountered by naturalists examining dead wood or watching for insects in open woodlands.

• Eudioctria spp.Similar minute size (6–8 mm) and general gestalt, but distinguished by shorter antennae and different perching behavior (flat leaves vs. twig ends). Eudioctria belongs to subfamily Stenopogoninae rather than Laphriinae.
• Andrenosoma fulvicaudumShared subfamily Laphriinae with similar larval ecology, but much larger (approximately 15 mm vs. 6–8 mm) with reddish abdominal markings and shorter antennae relative to body size.

• robber fly
• Laphriinae
• micropredator
• dead wood habitat
• wood-borer predator

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