Scarce Forest Horsefly (Hybomitra solstitialis)
Key Details
| Taxonomic Groups: | Invertebrate > insect - true fly (Diptera) > Soldier fly or ally |
| Red List Status: | Endangered (Not Relevant) [EN(nr)] |
| D5 Status: | Included in the baseline Red List Index for England (Wilkins, Wilson & Brown, 2022) |
| Section 41 Status: | (not listed) |
| Taxa Included Synonym: | (none) |
| UKSI Recommended Name: | Hybomitra solstitialis |
| UKSI Recommended Authority: | (Meigen, 1820) |
| UKSI Recommended Qualifier: | (none specified) |
| Red List Citation: | Drake, 2017 |
| Notes on taxonomy/listing: | (none) |
Criteria
| Question 1: | Does species need conservation or recovery in England? |
| Response: | Yes |
| Justification: | A single record from England in 2019 from Cothill Fen SSSI (SU46019987) and two records in 2011 from Cothill Fen and Dry Sandford Pit SSSI (SU46829958). Previous records (2008, unconfirmed) and prior to this 1971 (Holmsey Bog, Hampshire) and 1934 (Denny Lodge, Hampshire). |
| Question 2: | Does recovery/ conservation depend on species-specific actions? |
| Response: | Yes |
| Justification: | There are few records from specific rare habitats and these would heavily restrict the flies ability to become more abundant. With the lack of records at previously known sites over long periods, this may indicate the likelihood of stochastic extinction. |
| Question 3: | At a landscape scale, would the species benefit from untargeted habitat management to increase habitat mosaics, structural diversity, or particular successional stages? |
| Response: | No |
| Justification: | This species would not benefit from untargeted management |
Species Assessment
| Current step on the Species Recovery Curve (SRC): | 2. Biological status assessment exists |
| Recovery potential/expectation: | Low - Extinction debt |
| National Monitoring Resource: | Opportunistic - insufficient |
| Species Comments: | Rare, with few historical records, the older of these from the New Forest from which none have been made since 1971 & 1934. Biology is not fully understood, it is likely that larvae develop in unshaded waterlogged conditions. Sites of interest are small with little range for expansion. Latest records are from base rich stream fed fens. Females require large mammals for blood meals as a prerequisite for egg development. |
Key Actions
Key Action 1
Proposed Action: Tailored surveys of potential habitat in known localities to determine the population and species distribution, thus identifying areas if H. solstitialis is present
Action targets: 3. National Monitoring Plan agreed and implemented
Action type: Targeted monitoring
Duration: 2 years
Scale of Implementation: ≤ 5 sites
High priority sites: Cothill Fen SSSI, Berkshire (SU460998) & Dry Sandford Pit (SU468995)
Comments: A survey within the known flight period to encompass the areas where the previous two sightings have been made. Due to the extreme gap in records, surveying of older recorded sites in other areas such as the New Forest may also be useful. Once populations have been confirmed more specific actions may be identified.
Key Action 2
Proposed Action: Removal of reed and sedge that are filling shallow pools and runnels.
Action targets: 5. Remedial action identified
Action type: Habitat management
Duration: >10 years
Scale of Implementation: ≤ 5 sites
High priority sites: Cothill Fen SSSI, Berkshire (SU460998) & Dry Sandford Pit (SU468995)
Comments: Necessary to promote reproduction and to ensure that suitable habitat for larvae is protected and if possible expanded. On site guidance by specialist botanist to supervise Reed/Sedge clearance due to presence of protected Orchids within some areas of possible sites.
Key Action 3
Proposed Action: Rewetting and management of local fens that are not populated at the moment.
Action targets: 5. Remedial action identified
Action type: Habitat creation
Duration: 6-10 years
Scale of Implementation: ≤ 5 sites
High priority sites: Cothill Fen SSSI, Berkshire (SU460998) & Dry Sandford Pit (SU468995)
Comments: Sites of interest are small with little range for expansion, as the species is linked to specific rare habitats that heavily restrict the flies ability to become more abundant, this may allow further spread of limited populations.
Acknowledgment:
Data used on this website are adapted from Threatened species recovery actions 2025 baseline (JP065): Technical report and spreadsheet user guide (Natural England, 2025). Available here.