How does the water louse see?
The water louse (Asellus aquaticus) is a crustacean in the order Isopoda. Its eyes belong to the vision type Crustacean (mantis shrimp, crab).
Measured in this species: motion (flicker fusion). One measured dial: a value other than colour or sharpness is measured in this species; colour and sharpness are not measured here. Every value below carries its evidence level and sources; nothing is typed by hand.
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What stands out
- It has one receptor class for colour, so it sees brightness but no hue.
- Its sharpest vision resolves 0.05 cycles per degree: the finest stripe pattern it can tell apart from grey.
- It stops seeing flicker at 51.3 Hz, against 60 Hz for people in this dataset, so fast motion looks choppier to it.[6][7]
- Activity pattern: nocturnal.
The six dials
Evidence levels: how the tiers work. "Measured" means a value measured in this species; "Estimated" values come from a close relative or an eye-size formula.
| Dial | Value | Evidence | Sources |
|---|---|---|---|
| Colour | Colour receptors 1 receptor class: 520 nm (MWS (green)) ESTIMATE: receptor classes from opsin-gene presence in this species; lambda max per class from the measured class template of the nearest taxon (never from the gene itself) | Group default | [1][2] |
| Sharpness | Acuity 0.05 cycles per degree median of 1 relatives in order Isopoda: Natatolana borealis | Group default | [3] |
| Angle between facets 1.6° median of 1 relatives in class Malacostraca: Phronima sedentaria | Group default | [4] | |
| Eye type compound eye | |||
| Field of view | No value in the catalogue. | ||
| Sharp zones (foveas) | No value in the catalogue. | ||
| Night vision | Activity pattern nocturnal group default: mode of tier-A values in vision type V27 within phylum Arthropoda (1 species: Ligia exotica) | Group default | [1] |
| Rods vs cones no rods (invertebrate photoreceptors) | Group default | [1] | |
| Motion (flicker fusion) | Flicker fusion frequency 51.3 Hz median of 1 rows (no bright-light flag) (behavioural/whole-eye ERG rows; all rows: [51.3]) | Measured | [5] |
Related animals
- Isopod (Booralana tricarinata) same vision type
- Wharf roach same vision type
- Isopod (Glyptonotus antarcticus) same vision type
- Rock louse same vision type
- Peacock mantis shrimp same vision type
- Caridean shrimp same vision type
More crustaceans: all crustaceans with measured vision data.
Sources
- Longcore T. 2023. A compendium of photopigment peak sensitivities and visual spectral response curves of terrestrial wildlife to guide design of outdoor nighttime lighting. Basic Appl Ecol 73:40-50. doi:10.1016/j.baae.2023.09.002. doi.org/10.5281/zenodo.8432720
- NCBI Protein database: opsin records for arthropod and mollusc taxa (short esearch queries, one taxon x one opsin term), kept only curated RefSeq NP_ or PubMed-linked GenBank records. www.ncbi.nlm.nih.gov/protein
- Feller KD, Sharkey CR, McDuffee-Altekruse A, Bracken-Grissom HD, Lord NP, Porter ML, Schweikert LE 2021. Surf and turf vision: patterns and predictors of visual acuity in compound eye evolution. Arthropod Structure & Development 60:101002. doi.org/10.1016/j.asd.2020.101002
- Bagheri Z, Jessop A, Partridge J et al. 2022. A new computational model illuminates the extraordinary eyes of Phronima. PLOS Computational Biology. doi.org/10.1371/journal.pcbi.1010545
- Haarlem CS, Hynes C, Jackson AL, Mitchell KJ, O'Connell RG, Healy K. 2026. Pace of ecology drives the tempo of visual perception across the animal kingdom. Nature Ecology & Evolution (doi:10.1038/s41559-026-02994-7). Figshare dataset 10.6084/m9.figshare.30556475. doi.org/10.6084/m9.figshare.30556475
- Healy K, McNally L, Ruxton GD, Cooper N, Jackson AL. 2013. Metabolic rate and body size are linked with perception of temporal information. Animal Behaviour 86:685-696. Table 1. doi.org/10.1016/j.anbehav.2013.06.018
- Inger R, Bennie J, Davies TW, Gaston KJ. 2014. Potential biological and ecological effects of flickering artificial light. PLoS ONE 9(5): e98631. Table 3. doi.org/10.1371/journal.pone.0098631
Every value cites its sources (all sources). Data: catalogue-v1, built 2026-09-29. Accuracy notes: how accurate is this?