Phasia hemiptera is a tachinid

Tachinidae

Tachinidae is a large and rather variable family of true flies within the insect order Diptera, with more than 8,200 known species and many more to be discovered. There are over 1300 species in North America. Insects in this family are commonly called tachina flies or simply tachinids...

 fly

Fly

True flies are insects of the order Diptera . They possess a pair of wings on the mesothorax and a pair of halteres, derived from the hind wings, on the metathorax...

 found throughout Northern and Southern Europe

Europe

Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...

. It is a strongly sexually dimorphic species, males being more colourful with curved patterned wings. Like most tachinid flies, the female lays her eggs on other insect

Insect

Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...

s, the larvae then develop inside the living host, devouring it and eventually killing it. Its main hosts are the forest bug

Forest bug

The forest bug, Pentatoma rufipes, is a species of shield bug in the family Pentatomidae. It is a common and widespread species found in forests and woodlands worldwide. It is shiny dark brown with red-orange markings on its body and bright orange legs. It is shaped like an escutcheon-type shield,...

 Pentatoma rufipes in the spring, and the green shield bug Palomena prasina in the autumn.