Cactus Fly

The cactus fly, Odontoloxozus longicornis, is a member of the small family Neriidae, a group of elongate, stilt-legged flies most diverse in warmer regions of the Americas. It is closely tied to the desert ecosystems of the southwestern United States and northern Mexico, where its larvae develop exclusively in the rotting, fermenting flesh of cacti such as saguaro, cardón, and prickly pear.

Adults have a distinctively long-legged, wasp-like build with elongated antennae, an adaptation that allows them to navigate the narrow crevices and wounds in cactus tissue where they feed and lay eggs. They are strongly attracted to the smell of fermenting cactus rot, often arriving at a wound or decay site within hours of it forming.

By breaking down decaying cactus material, cactus flies and their larvae play a role in desert nutrient cycling, and the flies themselves become part of the diet of desert predators such as robber flies, spiders, and lizards.

• Slender, elongated body, roughly 10–15 mm, with a wasp-like appearance
• Long, stilt-like legs and long, thread-like antennae
• Reddish-brown to tan coloration with a somewhat shiny cuticle
• Wings held flat over the body, sometimes with a faint pattern
• Lookalikes: other stilt-legged flies (family Micropezidae) have a similar build but lack the strong cactus association and southwestern desert range

Cactus flies are found in arid and semi-arid habitats of the southwestern United States, including the Sonoran and Chihuahuan Desert regions, and into northern Mexico, wherever large columnar cacti such as saguaro grow. They are concentrated around wounded, rotting, or dying cactus tissue, which serves as both feeding and breeding site.

Adult cactus flies feed and mate at sites of cactus decay, using keen chemical detection to locate fresh rot, and are frequently observed clustering around wounds in saguaro or cholla where fermentation has begun. Larvae feed directly within the decaying, semi-liquid cactus tissue, consuming the microbe-rich rotting pulp. This decomposer role helps recycle the substantial biomass of large cacti back into the desert ecosystem once a plant is damaged or dies.

Females lay eggs directly into wounds or areas of soft rot on cactus tissue, and larvae hatch to burrow and feed within the decaying, fermenting pulp. Development through the larval stages proceeds relatively quickly given the warm desert temperatures and rich food source, with larvae eventually pupating either within the rot pocket or in the soil nearby. Multiple generations can occur in a year wherever suitable rotting cactus material remains available.