HYMENOPTERA | Parasitic Wasps

APOCRITA | Parasitica

'Parasitica' is an artificial (becoming obsolete) paraphyletic division of the suborder APOCRITA that, until very recently, has been the accepted term to separate the so-called 'parasitic wasps' from the stinging wasps, bees and ants. The various families within this group may be less well known than their Aculeate relatives but, collectively, they account for well over three-quarters of the 7,800 or so British hymenopteran species.

Although the members of the group as a whole are commonly referred to as 'parasitic wasps', the term is somewhat misleading as most parasites, such as fleas or mites for example, will cause their host a degree of discomfort, but would very rarely kill it. The larvae of most these wasps on the other hand may well start life as a parasite, but apart from the

gall-inducing species, will almost certainly end up killing their host as they develop, whether through starvation or from physically eating it. These species are parasitoid wasps.

Before breaking the group down into families, it's worth noting that there are actually two distinct types of parasitoid - the first is an ectoparasitoid whose larvae develop on the outside of the host species, and the second is an endoparasitoid whose eggs are deposited inside the host’s body.

At the point of attaching or inserting her egg(s), the female wasp will paralyse the host by injecting it with venom which has the added effect of modifying the tissues to overcome the natural immune system, thereby making it more nutritious for the developing wasp larva. Paralysis of the host typically works in one of two ways. The first is when the host is only partially affected, but soon recovers and continues to feed and develop normally until the wasp larva 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 usually have a relatively short development period, totally paralyses the host effectively killing it outright. The wasps that adopt this method are known as idiobionts.

In most cases, koinobionts are normally endoparasitoids with a longer larvae development period, but shorter adult life. These wasps usually target very specific host species. In contrast, Idiobionts are mainly ectoparasitoids who’s larvae have to eat the host reasonably quickly, but where the emerging adults tend to have a longer life. Although the biology varies, outright paralysis does not require special venom as used by the koinobionts, which normally allows for a wider range of host species.

The vast majority of these wasps are either very small and seldom seen, and/or almost impossible to identify from photos. There are also around thirty families to consider so, not surprisingly, only a few are going to be represented here.

The CHALCIDOIDEA superfamily, which is probably the most challenging of all insect groups, is represented in Britain by around 1800 mostly very small (< 3mm) parasitoid wasps that are notoriously difficult to identify even with microscopic examination. They had been traditionally separated into sixteen families, some of which comprised just a single or only a few species, while others, notably Eulophidae and Pteromalidae included many hundreds.

However, the taxonomic arrangement of the CHALCIDOIDEA is in the process of being updated following a recent review (Burks et.al.2022 - Journal of Hymenopteran Research 94:13-88) and reclassification of the Pteromalidae, which has elevated a large number of former subfamilies to family status. As such, the British list now extends to twenty-five families.

Under this revised structure, Eulophidae becomes the largest family with just over 500 listed species and, despite being reduced from fourteen to just five subfamilies, Pteromalidae is not that far behind with around 480. The Encyrtidae has 230, and the Eurytomidae, Mymaridae and Torymidae all have around 100 species, but of the nineteen remaining families, fifteen have 10 or fewer.

Five families are currently featured: Chalcididae, Diparidae, Eulophidae, Ormyridae and Pteromalidae.

Chalcididae

Chalcidid Wasps

Ormyridae

Ormyrid Wasps

Diparidae

Diparid Wasps

Pteromalidae

Pteromalid Wasps

Eulophidae

Eulophid Wasps

The CYNIPOIDEA superfamily comprises the gall-inducing cynipid wasps and inquilines, plus two rather different families; Figitidae, which includes around 130 small (> 4mm) species of koinobiont endoparasitoids of various holometabola (endopterygote) insect larvae, primarily Diptera; and the macrocynipoid (10mm) Ibaliidae, with just two rarely encountered parasitoids of wood-boring Siricidae sawfly eggs or early larvae.

The Cynipoidae family is now featured on two separate pages; the first being an extended page for some of the oak galls induced by the larvae of certain members of the Cynipini tribe, and the other for a few of the elusive adult wasps that I've managed to photograph. And, as of this latest update, I can now include an account for the Figitidae family.

Cynipidae

Oak Galls

Cynipidae

Gall Wasps

Figitidae

Figitid Wasps

The small DIAPRIOIDEA superfamily, which is only represented in the UK by two families, has only recently emerged following reclassification of the PROCTOTRUPOIDEA. The British members of this group were originally all placed together within the Diapriidae family, but that arrangement has now been updated as one particular genus has been separated to form the new Ismaridae family.

Diapriidae is an interesting family that is slightly less challenging than most of the others featured here as, despite their tiny size, the subfamily and respective genus can usually be determined. I've spent a fair bit of time researching these species, which is why this particular account now extends to two pages.

Diapriidae

Diapriid Wasps

Diapriidae

Diapriid Wasps - coastal species

This subsection includes two of the smallest families, Gasteruptiidae and Trigonalidae families.

Gasteruptiidae

Gasteruptiid Wasps

Trigonalidae

Trigonalid (Hyperparasitoid) Wasps

The ICHNEUMONOIDEA encompasses the two largest families of parasitoid wasps; Braconidae and Ichneumonidae, which collectively include close on 4000 species. With a bit of help, Braconids can usually be allocated to a subfamily from photos, and occasionally it may even be possible to suggest the likely genus. In that respect, I can currently represent the four subfamilies shown here, all of which are featured on a single page. The larger, more familiar Ichneumonids offer better opportunities from a photographer's perspective, as noted below.

Braconidae

Alsiinae

Braconidae

Braconinae

Braconidae

Rogadinae

Braconidae

Opiinae

Ichneumonidae (Ichneumon Wasps)

Generally larger and usually more colourful than their close relatives the braconids, ichneumon wasps are characterised by having a petiolate first metasomal segment (narrow 'waist'); long, filiform antennae with at least 16 segments, although usually 20 or more (whereas most, although not all, other wasp species have 13 or less); forewings with a thickened front edge as the costa and subcosta and/or radius are virtually fused, prominent pterostigma (stigma) and often with a distinctive areolet (second submarginal cell).

Descriptions use specific morphological terminology that can take a bit of getting used to. The most important terms relate to the structure of the body where the normal insect format of head, thorax and abdomen is replaced with head, mesonoma (middle segment) and metasoma (hind segment) as wasps have their 'waist' situated between the first and second segments of the abdomen. You might think that the narrow bit is 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. Consequently, the mesonoma includes the thorax and the propodeum, and the metasoma includes the abdomen from the second segment, which just to confuse matters is regarded as the first tergite. A final comment in this respect, is that the hymenopteran term 'gaster' is a specific rather than general term used for certain species such as ants and chalcid wasps.

The current checklist includes close on 2,600 species in well over 400 genera that are separated into 30 or more subfamilies. Not surprisingly, there are a lot of similar species, plus the fact that in many cases the sexes are dimorphic. Fortunately, the females can easily be distinguished where they have a long ovipositor, but there are also many, such as those in the Ichneumoninae subfamily, where the ovipositor can be very short or almost invisible.

Whilst a few of the more common species can be identified from photos with a bit of care, the vast majority can’t and, even with expert help, allocation to subfamily is very often the best that can be achieved. That said, I think I've been rather lucky in getting so many named including a few that are scarce or even rare.

Clicking any of the thumbnail images below will take you to a 'species account' that includes a variable amount of information with regard to the subfamily in general and, with as much detail as I can find, about the genus and/or species and its biology. I've also added appropriate notes in respect of whether the individuals that I've photographed have been positively confirmed or are simply deemed likely.

Footnote: the alternative family name of Darwin Wasps was proposed a few years ago by a group of ichneumonid specialists in an attempt to boost interest and improve recording. It's taken a little while, but it's catching on to the point that a few of the more common species have been named accordingly, such as the Yellow-tipped Darwin Wasp or Hedgerow Darwin Wasp for example. I can't see that they'll ever feature in scientific works as the vast majority of species will never be individually named, but they are included here where appropriate.

Banchinae