These beetles are fast-moving, relatively large predators that attack a wide range of insect prey; a few species eat seeds and play a role in reducing the weed seed bank in the soil. They are typically black in color, often with a metallic sheen. Since they are nocturnal, they often pass undetected in the farm and garden, even though they may be present in high numbers. At first glance they may be mistaken for the large, black ‘darkling’ beetles (Family: Tenebrionidae) that are active during the day (particularly in desert areas) but differ in having a much flatter abdomen. The larval stages develop in the soil (for up to 2 years, depending on species) and prey on other soil-dwelling organisms, including some pests.

Information from:  https://aces.nmsu.edu/pubs/insects/welcome

The flies in this family are parasitoids, i.e., the females lay their eggs on or in the bodies of other insects, and when the fly larvae hatch, they gradually consume the host until it dies, and the fly larvae pupate. Many tachinids attack larval moths and butterflies, although some species parasitize other insect groups (e.g., cucumber beetles). The adults often resemble large houseflies but have a bristlier abdomen. They sustain themselves on nectar and pollen, and so are often found on flowers during the summer.