Fen Mason-wasp (Odynerus simillimus)
Key Details
| Taxonomic Groups: | Invertebrate > insect - hymenopteran > Wasp |
| Red List Status: | (Not Relevant) [(not listed)(nr)] |
| D5 Status: | |
| Section 41 Status: | (not listed) |
| Taxa Included Synonym: | (none) |
| UKSI Recommended Name: | Odynerus simillimus |
| UKSI Recommended Authority: | Morawitz, F., 1867 |
| UKSI Recommended Qualifier: | (none specified) |
| Red List Citation: | (not listed) |
| Notes on taxonomy/listing: | Listed as Extinct (RDB1+) in Shirt (1987), but Falk (1991) provisionally placed it in the Endangered (pRDB1) category. |
Criteria
| Question 1: | Does species need conservation or recovery in England? |
| Response: | Yes |
| Justification: | Rediscovered in England in 1986, having been feared extinct. Very restricted geographical range. |
| Question 2: | Does recovery/ conservation depend on species-specific actions? |
| Response: | Yes |
| Justification: | Prey seems to be restricted to Hypera pollux, a weevil feeding on Fool's Water-cress Apium nodiflorum and Lesser Water-parsnipBerula erecta. |
| 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: | Not particularly applicable. The habitat conditions required are quite specific, with emergent aquatic umbellifers as hunting territory and sparsely vegetated, gently sloping ground within which to nest. |
Species Assessment
| Current step on the Species Recovery Curve (SRC): | 6. Recovery solutions trialled |
| Recovery potential/expectation: | Medium-high |
| National Monitoring Resource: | Opportunistic - sufficient |
| Species Comments: | The species already appears to be recovering from the point of feared extinction 40 years ago. |
Key Actions
Key Action 1
Proposed Action: Manage watercourses within the known range to promote growth of Fool's Watercress and Lesser Water-parsnip (the known food plants of the weevil prey of this species).
Action targets: 6. Recovery solutions trialled
Action type: Habitat management
Duration: 3-5 years
Scale of Implementation: ≤ 20 sites
High priority sites: Norfolk Broads; north-east Suffolk
Comments: Drains becoming blocked by Common Reed or other tall growth may need cyclical clearing in order to promote the growth and spread of the prey weevil's host plants. Translocation of those plants into new ditches close to potentially good nesting sites should also be trialled.
Key Action 2
Proposed Action: Resurvey sites where records are more than 10 years old to ascertain presence/absence to inform conservation management.
Action targets: 2. Biological status assessment exists
Action type: Status survey/review
Duration: 2 years
Scale of Implementation: ≤ 10 sites
High priority sites: Minsmere (last seen 2001), Snape Maltings, Suffolk (1999); Shoebury, Essex (2001); Howlands Marsh, Essex (2004); Alresford/Brightlingsea, Essex (2001/02).
Comments: Observations along the Suffolk and Essex coasts may represent dispersal from the core population in the Norfolk Broads and may be small, vulnerable to local extinction and in need of habitat enhancement if the wasp still persists.
Key Action 3
Proposed Action: Manage watercourses close to former sites in Suffolk and Essex, to promote growth of Fool's Watercress and Lesser Water-parsnip (the known food plants of the weevil prey of this species).
Action targets: 6. Recovery solutions trialled
Action type: Habitat management
Duration: 3-5 years
Scale of Implementation: ≤ 5 sites
High priority sites: Minsmere (last seen 2001), Snape Maltings, Suffolk (1999); Shoebury, Essex (2001); Howlands Marsh, Essex (2004); Alresford/Brightlingsea, Essex (2001/02).
Comments: Drains becoming blocked by Common Reed or other tall growth may need cyclical clearing in order to promote the growth and spread of the prey weevil's host plants. Translocation of those plants into new ditches close to potentially good nesting sites should also be trialled.
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.