Diptera: Calliphoridae
These are the “calyptrate” flies. They tend to be fast-flying, fat-bodied species that are often tricky to get close to in a field situation. Blow flies are well known for breeding in decaying organic material such as carrion, whereas the bristle flies are obligate parasites. There are about 50 species of blow fly and well over a 100 species of bristle fly in New Zealand. Other common calyptrate families are the Muscidae (e.g. house flies) with over 200 NZ species, and Sarcophagidae (flesh flies) with 4 species. We do not expect you to distinguish between these families in the field. Some of the bristle flies are distinctive, and you may wish to note these down in your data sheets. Others, however, are very similar to bluebottles or muscids. For simplicity sake, it is easier to treat flies you see of this type simply as “big flies”. Naturally, Murphy’s law prevails and some calyptrate flies are diminutive and are likely to be included in “small flies”. As stated earlier, such anomalies are expected and at this stage we are more interested in the mechanism of pollination rather than the taxonomy of flies.