Introduction

Parasitic insects (also known as parasitoids) are insects whose immature stages (larvae) develop by feeding on or in the bodies of their host arthropods, which are usually other insects. Unlike true zoological parasites, parasitic insects kill their hosts. However, parasitic insects are unique, because it is the immatures that kill the host. Parasites are usually defined (see window on types of parasites) by the feeding habit of the immature stage (egg. larval, pupal parasite, etc.), where the egg is laid (inside the host = endoparasite; outside the host = ectoparasite), and whether one or more parasite progeny emerge from the host (solitary vs. gregarious). Nearly all parasite immatures develop on or in a single host. Parasites are holometabolous, having complete development (egg. larval, pupal and adult stages). Adult parasites are free living; some species will feed on hosts, in addition to ovipositing in or on the hosts. In the world of parasites, only females are significant players, as they are the ones that find and attack hosts. For some species, males are not known to exist.

The number of species of parasites is unknown and speculative, ranging from an estimate of 800,000 to as many as 25% of all insects. Far and away, the greatest diversity of parasites is found in the Hymenoptera. However, many Diptera are parasites, and rare representative taxa are also found in the Coleoptera, Lepidoptera and Neuroptera. Strepsiptera are true zoological parasites, as they do not kill their hosts.