One way to obtain quality butterfly and moth specimens is to rear the adults from the caterpillars. Amateur Lepidopterists (Butterfly and Moth Collectors) have greatly contributed to the knowledge of caterpillar food plants through attempts to rear them to adults. Last Summer (2011) I reared some Milkweed Tiger Moth Caterpillars that went into pupation and spent the winter as fuzzy pupae. I checked them periodically for emergence, but no moths emerged. One day this spring (2012), I observed several flies in the rearing container. The flies were tachinids. Most tachinid flies are parasitoids of other insects. No moths were to emerge as a result of my efforts. All cocoons had been parasitized.
Some tachinids, such as the genus Lespesia, are parasitoids of several caterpillar species including both the Monarch Butterfly caterpillars and Milkweed Tiger Moth Caterpillars. Tachinid parasitoids are quite common and known to disappoint hobbyists trying to rear Monarch Butterflies. In some areas, rates of parasitism exceed 10 percent of the Monarchs.