Summary: As many of you already know, nature can be cruel. The Tachinid fly lays its eggs on, nearby, or inside a host insect. The Tachinid fly larva eats its living host from the inside out. A cruel death, but that's nature for you.
The reproduction method of the Tachinid fly may sound cruel, but this fly plays an important part in limiting the populations of other insects often considered pests. The Tachinid fly is actually a diverse species of insects that share the same name. Tachinid flies are generally about the size of houseflies. There are over 1300 different species in North America alone. The flies can be large or small, colorful or drab. There are some species of Tachinid flies that are bright orange, metallic blue, or green, and others are plain looking grey or black. There are also Tachinid fly species that mimic wasps.
Tachinid flies are technically parasitoids rather than parasitic, the difference being that parasitoids usually kill their host while parasites usually do not. Adult flies feed on nectar or the honeydew produced by aphids, but the larvae of Tachinid flies feed on a living host.
Adult female Tachinid flies use various methods to transport their eggs to a host. They can lay their eggs directly into the host by means of an ovipositor, or lay the eggs on a nearby leaf so the host ingests the eggs which develop in the stomach of the host. Sometimes the eggs develop inside the female Tachinid fly and she gives birth to live young that crawl to a host and enter the body through soft tissue. A menu of choices is their key to success.
Caterpillars, larvae of moths, grasshoppers, beetles and beetle larvae, and many kinds of true bugs are hosts of Tachinid fly larvae. Some destructive insects like sawflies caterpillars and cabbage loopers are killed by Tachinid fly larvae, but sometimes useful insects like silkworms are also subjected to attack. Tachinid flies are sometimes used as part of an integrated pest management strategy to limit the numbers of pest insects. In that Tachinid flies are not sold commercially, introduction of the fly to control other unwanted insects must be done under the control of a government agency. Said permit holder might, for example, release a batch of Tachinid flies into a crop field to control an unwanted insect pest in the hope that the Tachinid fly will perform its method of biological pest control. This can be effective, but sometimes fails when the flies attack a non-targeted species of insect such as the larvae of beneficial butterflies. However, there have been some successful release stories including the effects of Tachinid fly on the Eastern Tent Caterpillar. It is a tough balancing act.
Here's a note to crickets. Tachinid fly females can locate crickets by listening to their chirps. The Tachinid fly has a unique hearing system that is located not on their head, but on their pro-thorax, which is the body segment to which the front legs are attached. Their ears have connected tympanum (the eardrums) and a coding system which is different from any other species. Their hearing system is being studied to see if it can be applied to human technology.