In northern Europe at least, O. obscuratus is usually readily recognisable as it is the only frequently encountered species which has copious yellow or creamy markings.However, there are 2 pitfalls:

1. Similar appearance of Ophion forticornis
2. Dwarf forms of O. obscuratus that can superficially resemble other Ophion species

Distinguishing O. forticornis from O. obscuratus
O. forticornis:

• is rarely collected in Britain (but is seemingly more frequent in some other countries)
• is restricted to sand dunes
• has a much greater gap between the ocelli and eyes
• has a rather slenderer metasoma (abdomen)

Dwarf forms of O. obscuratus
O. obscuratus is known to occur in 3 distinct morphs in Britain (Brock, 1982):

• spring form
• 'autumnal dwarfs'
• 'autumnal giants' – the most frequent form

Whether they really belong to the same species is not certain.The spring and dwarf forms have been reared from a variety of low-feeding moth larvae of the family Noctuidae, such as Mythimna and Lycophotia. The autumn (and winter) flying giants, have never been reared. The host must almost certainly be a very common, yet hardly reared noctuid larva.Dwarf forms of O. obscuratus that lack the yellow markings superficially resemble other Ophion species, such as:

• O. crassicornis
• O. parvulus

However, they can still be recognised as O. obscuratus by the:

• yellow apex to the stigma
• the noticeably paler stripes along the inner edges of the eyes

Ophion obscuratus is one of the more conspicuous species of Ichneumonidae, a very species-rich family of parasitoid wasps.As parasitoids develop, their larvae feed on their host, and eventually kill it. There are around 6,000 species of parasitoid wasps in the UK. Most are parasitoids of other insects such as moths and butterflies - especially their eggs and caterpillars - flies, beetles, greenflies, whiteflies, scale insects and other wasps.Some parasitoid wasps are used commercially as biological controls of pest species. Importantly, their control is specific, limited to only one or a few species, with most wildlife left unaffected. Encarsia formosa, for example, is used worldwide to control whiteflies, a greenhouse pest that affects many crops.

• Ophion obscuratus is widely distributed across the Palaearctic (Europe and temperate Asia).
• The apparent range of O. obscuratus may have been counfounded with those of similar species (records from Argentina, for example, are certainly erroneous). Nevertheless, this is certainly a widespread and frequently abundant species.
• Across Britain, O. obscuratus is one of the most frequently trapped nocturnal ichneumonids. It can be found in a variety of habitats and is particularly abundant in gardens.