River-shore Cranefly (Rhabdomastix japonica)
Key Details
| Taxonomic Groups: | Invertebrate > insect - true fly (Diptera) > Fly |
| Red List Status: | (Not Relevant) [(not listed)(nr)] |
| D5 Status: | |
| Section 41 Status: | (not listed) |
| Taxa Included Synonym: | (none) |
| UKSI Recommended Name: | Rhabdomastix japonica |
| UKSI Recommended Authority: | Alexander, 1924 |
| UKSI Recommended Qualifier: | (none specified) |
| Red List Citation: | (not listed) |
| Notes on taxonomy/listing: | (none) |
Criteria
| Question 1: | Does species need conservation or recovery in England? |
| Response: | Yes |
| Justification: | The fly has a widespread but sparse distribution from Westmorland in the North to Dorset and Devon in the South. Nine English records in the past 25 years. |
| Question 2: | Does recovery/ conservation depend on species-specific actions? |
| Response: | Yes |
| Justification: | The fly is associated with sandy deposits on the banks of Rivers with low vegetation, the larvae can be found 4-5 cm below the surface and could be at risk form extraction, flooding and human disturbance. |
| 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: | Yes |
| Justification: | Retaining river flow patterns, avoidance of damming or abstraction that may affect bankside sandy deposits |
Species Assessment
| Current step on the Species Recovery Curve (SRC): | 2. Biological status assessment exists |
| Recovery potential/expectation: | Low - Life history factor/s |
| National Monitoring Resource: | Opportunistic - insufficient |
| Species Comments: | Can be mistaken for R. laeta so care will be needed in any surveying that is carried out. |
Key Actions
Key Action 1
Proposed Action: Surveying of previously occupied sites to establish if populations still exist before further targeted actions can be assessed
Action targets: 3. National Monitoring Plan agreed and implemented
Action type: Targeted monitoring
Duration: 2 years
Scale of Implementation: ≤ 20 sites
High priority sites: Most recent records are from Dorset, 2018, Mapperton (SY505986), South Devon, 2015, R. Otter at Tipton-St-John (SY0992), Cheshire, 2009, Moston (SJ397704), 2007, Somerford CP (SJ832652), Cumberland, 2008, 2005 Kellwood (NY526637) Westmorland, River Eden (NY771133)
Comments:
Key Action 2
Proposed Action: Monitoring of potential sites and surroundings outside of known areas to ascertain/ identify areas where the fly may be present. (Utilisation of Cranefly recording Scheme)?
Action targets: 3. National Monitoring Plan agreed and implemented
Action type: Targeted monitoring
Duration: 2 years
Scale of Implementation: National
High priority sites: Those already stated and other similar points on the same rivers, plus exploratory surveying of suitable sandy deposits on suitable flowing rivers
Comments: Relies on working with the Recording Scheme and promotion of this as a project for Dipterists to become involved with. Identification may rely on specialists. Underlying catchment geology, usually sandstones, which provide the base material upon which the bars are composed. Sediment characterisation of the existing sites will aid this. proportions and size of sand particles will assist, especially if large locations can be precise.
Key Action 3
Proposed Action: Advice and support for local landowners, farmers and agency staff in areas where populations are confirmed or found.
Action targets: 4. Autecology and pressures understood
Action type: Landscape/catchment/marine management
Duration: >10 years
Scale of Implementation: ≤ 20 sites
High priority sites: Most recent records are from Dorset, 2018, Mapperton (SY505986), South Devon, 2015, R. Otter at Tipton-St-John (SY0992), Cheshire, 2009, Moston (SJ397704), 2007, Somerford CP (SJ832652), Cumberland, 2008, 2005 Kellwood (NY526637) Westmorland, River Eden (NY771133)
Comments: Liaising with local landowners and farmers in relation to water abstraction, slurry, run-off, cattle drinks and potential of ingress by avermectins and other harmful chemicals that may kill larvae or make areas uninhabitable.
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.