The larvae of Tachinid flies are parasitoids, developing in or on other insects. This means they perform the ecosystem service of biological control. They utilise a wide range of hosts, including beetle grubs, grasshopper eggs, earwigs and bee and wasp larvae. The adult flies have adapted to the different hosts the larvae use. Those whose young are raised on insects that live underground or in concealed spaces, such as beetle grubs, lay their eggs on the ground in a habitat that may have hosts. They lay thousands of eggs, that immediately hatch and burrow to find a host. This adaptation is used as there is high risk involved for eggs, that may be eaten or desiccate. Many eggs means some of the larvae may survive, immediate hatching means the active larvae can find a place to hide.

Others lay micro eggs onto leaves, these are eaten by caterpillars and the eggs hatch when in the digestive tract, where they stay until they are ready to pupate. Others lay their eggs onto the back of a host, some produce a glue to stick the eggs to the host, others have eggs that have small spikes that stick into the host like a dart. A fourth group lay eggs into the host. Their ovipositor is adapted to drill into the host, or they lay the eggs directly into the abdominal opening. There is less risk for these eggs, so they only lay a couple of eggs, allowing them to invest more resources into each egg. They also are not at risk of predation, so the eggs “incubate” and hatch after a period of time.

The larvae have adapted their mouthparts to suit their environment. Those that live on the outside of a host (ectoparasitoids) have hook like mouthparts, while those that live on the inside (endoparasitoids) have cutting or drilling tools as part of their mouthparts.

This amazing group of flies have a lot to offer us and are truly fascinating.