Conopidae

Thick-headed Flies are impressive insects, often very unlike any other fly most people will have encountered and have interesting life histories. They comprise the Conopidae family and many species are excellent wasp mimics. Structurally, they have certain anatomical features, suggesting they are closely related to hoverflies.

Thick-headed Flies are parasitic insects and the larvae feed internally within Aculeate Hymenoptera (Bees and Wasps) with some species known to attack Orthoptera (Crickets and Grasshoppers etc). The adults are avid nectar feeders and regularly visit flowers and are good pollinators.

Most Thick-headed Flies wait on or near flowers for their selected host species to arrive. On finding the correct host, they take good hold and pierce the body while in flight, quickly depositing an egg inside.

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The egg hatches and the larva feeds off the host's abdominal contents, usually for about 10 days, effectively hollowing it out and filling almost the entire abdominal cavity. The larva pupates inside the host becoming an adult fly the next summer. Parasitised bees appear to change the behaviour and tend to stay outside the nest more than other workers, often remaining outside even in very cold weather.

Known species with Nottinghamshire records

A total of 11 species are known from Nottinghamshire, but there are modern (post-1960) records for just six of these. These are illustrated below and for which we provide distribution maps, based on records we have been sent by numerous invertebrate recorders and organisations. One species (Thecophora atra) is believed not to have been seen in Nottinghamshire since the 1950's, so just fails to qualify as having produced a modern record.

A full list of Conopidae recorded in VC56 Nottinghamshire is listed below.

Conops flavipes (Linnaeus, 1758), Conops quadrifasciatus (De Geer, 1776) , Conops vesicularis (Linnaeus, 1761), Conops strigatus (Wiedemann in Meigen, 1824), Myopa buccata (Linnaeus, 1758), Myopa polystigma (Rondani, 1857), Myopa occulta (Wiedemann in Meigen, 1824), Myopa testacea (Linnaeus, 1767), Physocephala rufipes (Fabricius, 1781), Sicus ferrugineus (Linnaeus, 1761) and Thecophora atra (Fabricius, 1775).

Species with historical records only, include Conops strigatus, Myopa buccata, Myopa polystigma, Myopa occulta and Thecophora atra.

Conops flavipes (Linnaeus, 1758)

Nottinghamshire distribution: Frequent in the north-west of the county, with most records coming from the Mansfield and Sherwood Forest areas. The county's most northerly records are from Clumber Park and Dyscarr Wood, near the border with Derbyshire.

A record from Attenborough NR, seems to indicate that Conops flavipes is more widespread than current records would suggest, yet it is absent from some well recorded sites along the Trent Valley. Recorder-bias, may be playing a part in the apparent range of this Conopid.

Flight period: The dated records we have, give a flight period from the middle of July through to late August.

Conops quadrifasciatus (De Geer, 1776)

Nottinghamshire distribution: Certainly one of the most regularly encountered of all Nottinghamshire's Thick-headed Flies, Conops quadrifasciatus is known from Trent Valley sites south and east of Nottingham, but is once again most numerous in the Sherwood Forest and Clumber Park areas.

Like the previous species, Conops quadrifasciatus will often be found nectaring at the flowers of Creeping Thistle along the edges of woodland, rides and clearings.

Flight period: Overall, this Conopid flies from around the middle of July, through August and into the first week of September. Over the past few years, Pauline Bradford has sent us some extremely useful data regarding Conops quadrifasciatus from Dyscarr Wood. Pauline's data suggests that peak numbers occur during August and that it had an exceptional year in 2014.

Conops vesicularis (Linnaeus, 1761)

Nottinghamshire distribution: The records we have, indicate that this large and impressive species is totally confined to the Sherwood Forest area of the county. It clearly prefers wooded locations and is not solely restricted to deciduous woodland and will occur in Pine plantations, as long as there is a suitable nectar source.

There are known records for Clipstone Old Quarter, Sherwood Heath SSSI and from Clumber Park.

Flight period: Inclusive flight dates we have (May 1st - July 22nd) suggest that Conops vesicularis flies from early May, through to middle of July.

Myopa testacea (Linnaeus, 1767)

Nottinghamshire distribution: Myopa testacea appears to be a rare Conopid in Nottinghamshire, with only three recent records. It was recorded from Attenborough NR in 2009 and 2010 (Rogers, R.) and most recently at Market Warsop Cemetery in April 2017 (Pendleton, T.A. and Pendleton, D.T).

Flight period: This is a Spring flying species, with Nottinghamshire's recent records all falling between April 12th and 18th.

Physocephala rufipes (Fabricius, 1781)

Nottinghamshire distribution: Has much the same Nottinghamshire distribution as Conops flavipes and Conops quadrifasciatus. Physocephala rufipes has been recorded from Attenborough NR in south Nottinghamshire, to the Idle Valley NR near Retford.

It occurs in a range of sites, from areas of heathland at Walesby, Oak Tree Heath and Clumber Park, to wetland locations like the Idle Valley NR and Attenborough NR. Like all Conopids, the adults are regularly found nectaring at patches of Creeping Thistle.

Flight period: There is an isolated record from Attenborough NR for June, but apart from that date, most dated records we have suggest a flight period from late July, continuing into August.

Sicus ferrugineus (Linnaeus, 1761)

Nottinghamshire distribution: Widespread in western Nottinghamshire and with no real indication as to why it apparently shows a restricted range in VC56, other than recorder-bias.

It occurs at a wide range of sites, where there is a profusion of flowers which are visited for their nectar, but is probably more frequently found occurring along sheltered woodland rides.

Flight period: Found during June and July, with some individuals remaining into August.