Silent Crickets, Deadly Flies: New Host Records Reveal Hidden Parasitoid Strategies in Brazil

Deep in the leaf litter of Brazil’s Atlantic Forest, a quiet arms race has been unfolding largely unnoticed by science. True crickets, a group boasting more than 6,000 species worldwide, are routinely hunted by parasitoid flies of the family Tachinidae, insects whose larvae devour their hosts from the inside. Yet for all the attention lavished on crickets as models in bioacoustics, behavior, and evolution, the flies that stalk them have remained frustratingly obscure. A new study published in the Journal of Orthoptera Research has now changed that, documenting seven new host-parasitoid records from Brazil and assembling the most complete picture to date of how these deadly flies find, attack, and exploit their chirping victims.

The research team, led by specialists working with specimens deposited in the Museu de Zoologia da Universidade de São Paulo and the collections of São Paulo State University in Botucatu, reared tachinid flies from crickets collected across multiple Brazilian states. The specimens included crickets gathered as far back as 1989 through 1991, kept alive in the laboratory for behavioral observations, from which the parasitoid flies eventually emerged. Additional records came from material collected in Rio Grande do Sul in 2012 and 2013. By pairing painstaking morphological work with a sweeping review of the literature, the authors have delivered both an illustrated identification key to the fly genera involved and an annotated catalog of every published record of tachinid parasitism in true crickets.

The scale of the synthesis is striking. At least ten species of tachinid flies, spread across four New World genera, are now known to parasitize at least 31 species of crickets in the families Gryllidae, Oecanthidae, and Phalangopsidae. All confirmed records come from the Nearctic and Neotropical regions, with no published evidence of these interactions elsewhere in the world. The four culprit genera, Anisia, Calodexia, Exoristoides, and Ormia, each pursue crickets in a radically different way, and it is this diversity of attack strategies that gives the new study its broader evolutionary significance.

The most famous of these parasitoids is undoubtedly Ormia ochracea, a fly that has become a legend among sensory biologists. Female Ormiini flies possess elaborately modified tympanal organs on the prothorax, essentially ears, that allow them to eavesdrop on the mating calls of male crickets and home in on their singers with pinpoint accuracy. In some field cricket populations, this parasitism acts as a potent selective pressure, shaping the density and distribution of different male morphs. Yet the new catalog reveals that only three Ormia species, O. ochracea, O. depleta, and O. dominicana, have adapted to detect the lower-frequency calls of true crickets, even as their relatives specialize on katydids and mole crickets that sing at higher pitches.

The Brazilian records add fresh chapters to this story. In São Lourenço do Sul, Rio Grande do Sul, the team reared a male and a female of O. ochracea from two males of the cricket Anurogryllus (Urogryllus) toledopizai, a new host record for the fly in the Neotropical region. Anurogryllus males are renowned for their long, loud trills, making them conspicuous acoustic targets. Significantly, the host genera parasitized by Ormia, Hapithus, Anurogryllus, Gryllus, and Teleogryllus, are all recognized as accomplished singers, underscoring the acoustic nature of this evolutionary relationship.

Far less glamorous but equally fascinating are the blondeliine genera Anisia and Calodexia, whose taxonomy has long been a tangle. The team’s new records span remarkable ground. A female Anisia was reared from an undescribed Aracamby species collected in Caraguatatuba, São Paulo. Several Calodexia species or near-variants emerged from crickets across São Paulo, Paraná, Rio de Janeiro, and Bahia, including one male reared from Guabamima lordelloi, a specimen that turned out to be the very holotype of the species, preserved at the São Paulo zoology museum. In an added surprise, the researchers also recovered three females of Stylogaster, a genus of thick-headed flies in the family Conopidae, from the same Pizacris crickets parasitized by Calodexia in São Fidélis, hinting that multiple parasitoid lineages converge on these litter-dwelling hosts.

What makes Calodexia particularly remarkable is its hunting method. These flies are intimately associated with army ants, and gravid females perch on foliage ahead of advancing ant swarms, waiting for orthopteroids flushed from the leaf litter. When a cricket bolts, the fly darts after it and glues an incubated, membranous egg carrying a ready-to-hatch larva directly onto the host’s cuticle. Because this strategy relies on vision rather than sound, Calodexia can exploit both chirping and completely silent crickets alike. That may explain why the genus, endemic to the Neotropics and encompassing 40 valid species, shows the widest host range of the four groups, hitting wingless, songless males of Aracamby, Eidmanacris, and Pizacris as readily as singing species of Anurogryllus, Eneoptera, and Guabamima.

Anisia, by contrast, appears to pursue a strategy borrowed from an entirely different playbook. Females of several species deposit minute, unpigmented, incubated microtype eggs on the host’s food, which are then swallowed by the unsuspecting victim. Notably, Aracamby males lack the forewing structures, such as the mirror and harp, needed for calling songs, yet they still perform low-frequency courtship songs. This raises an intriguing question: can Anisia females detect such faint vibrations, or do they instead track chemical cues? Crickets are known to communicate chemically, and the authors suggest that host-derived odorants, rather than diet-based cues, may guide these flies, a hypothesis that awaits testing in the field.

The fourth genus, Exoristoides, adds yet another puzzle. Only one species, E. johnsoni, has been reared from true crickets, parasitizing hosts across the United States and southern Canada, while its relatives attack cockroaches. Despite sharing the same ovoviviparous egg and larval types as the sound-tracking Ormiini, Exoristoides species possess no ears for eavesdropping. Clues may come from Triarthria setipennis, a tachinid parasitoid of earwigs shown in laboratory experiments to oviposit in response to chemical scents from its hosts. Whether Exoristoides females similarly follow chemical trails through the night remains one of the study’s tantalizing open questions.

Taken together, the seven new Brazilian records and the annotated catalog recast true crickets not merely as singing victims of one famous fly, but as hosts exploited through at least three distinct parasitoid playbooks: acoustic ambush by Ormia, ant-following visual pursuit by Calodexia, and probable chemical subterfuge by Anisia and Exoristoides. Each strategy unlocks a different slice of cricket diversity, from raucous trillers to voiceless litter-dwellers. The illustrated identification key and host catalog now give entomologists the tools to untangle these interactions across the Americas, and the authors hope that future work on the poorly known biology of Anisia and Exoristoides will finally illuminate the full spectrum of the ancient and deadly dance between flies and crickets.

Subject of Research: Parasitoid tachinid flies attacking true crickets in Brazil and their host location strategies

Article Title: Parasitoid flies ( Diptera , Tachinidae ) in true crickets ( Orthoptera , Grylloidea ): New host records from Brazil, identification key to parasitoids, and revision of host-parasitoid interactions

Article References: Gudin, F. M., Campos, L. D. D., Redü, D. R., & de Mello, F. D. A. G. (2024). Parasitoid flies (Diptera, Tachinidae) in true crickets (Orthoptera, Grylloidea): New host records from Brazil, identification key to parasitoids, and revision of host-parasitoid interactions. Journal of Orthoptera Research, 33(1), 41-58. https://doi.org/10.3897/jor.33.108456

Image Credits: AI Generated

DOI: 10.3897/jor.33.108456

Keywords: Tachinidae, Grylloidea, parasitoid, Ormia ochracea, Calodexia, Anisia, Exoristoides, crickets, Brazil, oviposition strategies, host-parasitoid interactions, bioacoustics