HYMENOPTERA | Parasitic Wasps

APOCRITA | Parasitica

Although the term parasitic is commonly used to describe this group of wasps, it is both misleading and incorrect, as a true parasite such as a flea or tick may cause its host a degree of discomfort, but would rarely kill it. The larvae of a parasitic wasp on the other hand will definitely harm its host and will almost certainly kill it and, consequently, it should be referred to as a parasitoid species.

There are two types of parasitoid - the first is an ectoparasitoid whose larvae develops on the outside of the host species, and the second is an endoparasitoid where the eggs are deposited inside the host’s body.

Most parasitic wasps inject venom into the host when, or just before, laying their egg(s) in order to paralyse it and to modify its tissues, which overcomes the natural immune system thereby making it more nutritious for the developing wasp larvae. Paralysis of the host takes two forms. The first is when the host is only partially affected, but soon recovers and continues to feed and develop until the wasp larvae reaches maturity, at which time it will normally be eaten. The wasps that use this strategy are known as koinobionts. The other form, where the wasp’s larvae only have a short development period, totally paralyses the host effectively killing it outright. The wasps that adopt this method are known as idiobionts.

Koinobionts are normally endoparasitoids with a longer larvae development time, but shorter adult life. These wasps target very specific host species. Idiobionts on the other hand are mainly ectoparasitoids who’s larvae have to eat the host relatively quickly, but where the emerging adults have a longer life. Outright paralysis does not require special venom as used by the koinobionts, which allows for a wider variety of host species.

The various families within this group may be less well known than their aculeate relatives - the bees and stinging wasps - but collectively, they actually account for over three-quarters of the 7,800 or so British hymenopteran species.

Clicking any of the photo thumbnails immediately below takes you to an overview of the family followed by a brief 'species account' and some further images. The large Ichneumonidae family is dealt with in a not dissimilar way except that the thumbnails take you straight to the 'species account' with varying amounts of information.

Eulophidae

Chalcid Wasps

Trigonalidae

Hyperparasitoid Wasps

Chalcidae

Chalcid Wasps

Gasteruptidae

Gasteruptid Wasps

Cynipoidae

Gall Wasps

Braconidae

Braconid Wasps

Ichneumonidae (Ichneumon / Darwin Wasps)

Generally larger and more colourful than their close relatives the braconids, ichneumon wasps are characterised by their very narrow ‘waist’ and long antennae of at least 16 segments. Whilst a few of the more common species can be identified from photos, the vast majority can’t and, consequently, even with expert help, allocation to subfamily is about the best that can be achieved and even that’s quite difficult as there are around 30 subfamiles!

Not only are there literally hundreds of similar species, but in many cases the sexes are dimorphic just to make identification even harder. Determining the sex though is usually a bit more straightforward as the females often have a long and conspicuous ovipositor.

Whilst the standard terms for an insect’s three main body parts are head, thorax and abdomen, experts tend to use the words head, mesosoma (middle segment) and metasoma (hind segment) when dealing with wasps as their ‘waist’ falls between the first and second segments of the abdomen. You might expect the narrow bit to be the first part of the abdomen but it’s actually the second – the first segment is called the propodeum and is attached to the back of the thorax.

The majority of the British ichneumonid species are parasitoids of butterfly and moth larvae, others attack sawflies, and some specialise in beetles, flies or spiders.

In an attempt to promote better awareness and recording of the various species, it has recently been proposed that the common name of the family be changed to Darwin Wasps to reflect the pivotal role they played in convincing Charles Darwin that not all of creation could have been created by a benevolent god. The name is catching on to the point that many of the more well-known species are being given common names such as Yellow-tipped Darwin Wasp or Hedgerow Darwin Wasp.