Tachinid Fly

Tachinid flies make up the family Tachinidae, one of the largest and most ecologically important fly families, with many thousands of species distributed worldwide. Adults are typically stout-bodied and covered in stiff bristles, especially toward the tip of the abdomen, giving them a somewhat rugged, spiky appearance compared to the smoother bodies of house flies and blow flies to which they are related.

The defining feature of the family is a parasitic larval stage: female tachinids lay eggs on or near a host insect, most commonly caterpillars, beetle larvae, true bugs, or grasshoppers, and the hatching larvae burrow into the host's body to feed internally, eventually killing it as they complete development. Different species use different delivery methods, including gluing eggs directly to the host's skin, depositing eggs on foliage the host is likely to eat, or even injecting live larvae directly into the host.

Because of this parasitic relationship, tachinid flies are considered important natural regulators of many insect populations, including numerous agricultural and forest pests, and are frequently studied and sometimes intentionally introduced as part of biological pest management programs.

• Robust, bristly fly, generally 6–15 mm long, often gray, black, or brown, sometimes with an orange or reddish abdomen
• Abdomen typically bears a row of prominent stiff bristles near the tip, a key identifying feature of the family
• Head is broad with large eyes and a strongly bristled face
• Wings are clear and held flat over the body at rest, with a fast, direct flight similar to a house fly
• Distinguished from house flies and blow flies mainly by the heavier bristling, especially the conspicuous bristles at the abdomen tip

Tachinid flies are found nearly worldwide in habitats ranging from gardens and meadows to forests and agricultural fields, wherever suitable host insects are present. Adults are commonly seen visiting flowers, especially those in the carrot and daisy families, for nectar, while searching nearby foliage for host caterpillars or other insects on which to lay eggs. Activity peaks during the warmer months when host insect populations, particularly caterpillars, are most abundant.

Adult tachinid flies feed on nectar and pollen, making them incidental pollinators of many flowering plants, while females devote much of their activity to locating suitable host insects for their parasitic larvae. Depending on the species, eggs may be glued directly onto a host's body, scattered on foliage for the host to accidentally ingest, or, in some species, larvae are deposited alive directly onto or into the host. Within the ecosystem, tachinid flies serve as important natural enemies of caterpillars, beetle larvae, and other insects, helping to regulate the populations of many species that would otherwise damage garden and agricultural plants.

Depending on the species, eggs are laid on the host's body, on foliage likely to be eaten by the host, or as live larvae deposited directly onto or into the host. Once inside, the tachinid larva feeds on the host's internal tissues while carefully avoiding vital organs at first, allowing the host to continue living and feeding for a time before the parasite completes development and the host dies. The mature larva then exits the host to pupate, either in the soil or within the remains of the host, and adults emerge after a period of days to weeks depending on temperature, with many species producing multiple generations per year in warm climates.