The ichneumon wasps are solitary insects. They are parasites and parasitoids of other insects especially of butterflies and moths. The difference between the two types is that parasites live in or on other species feeding on them without killing them. Parasitoids end up killing their host.
There are even some ichneumons which are hyperparasitoids that is they are parasitoids of parasitoids. These have very complicated life cycles which are difficult to study and unravel.
The ichneumons are well adapted to live on the caterpillars of butterflies and moths and play an important role in controlling their numbers. Some species have been recorded as living on other insects including beetles, aphids and spiders.
Being hymenopterans ichneumons share many features with sawflies, bees, wasps and ants.
The ichneumon family is a species rich family with over 36,000 species. Just twenty nine species have been recorded in Malta although many more are bound to be discovered as few studies of this family have been carried out in the Maltese islands.
This is understandably a diverse group of insects. They vary in size from just three to one hundred and thirty millimetres long. Most are slender with the females having a long ovipositor which is used to drill into the host and to lay eggs inside its body.
While some ichneumons lay their eggs in a wide variety of host species others are very specific and target just one or two related species. Some of the latter species are used as biological control agents. These controlling agents are bred specifically to be released in areas where its host species has become a pest. Biological control systems replicate nature and for them to be successful pesticides should not be used as these could kill both the pest species as well as its controlling agent.
This article was published in the Times of Malta on 1 January 2015