Skip to main content

Thank you for visiting You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

  • Letter
  • Published:

Robust judgement of inter-object distance by an arthropod


Animals use several strategies for depth vision, reflecting the constraints imposed by body size, the structure of the visual system and the visual geometry of the environment1. Arthropods in particular have restricted depth perception, because they are small and possess closely set, low-resolution compound eyes. Yet, here we show that fiddler crabs defending their burrows from conspecifics can judge how close other crabs are to their burrow. When confronted with small dummy crabs, the burrow owners assess the dummy's position and motion relative to their burrow and not relative to themselves—in other words, by using an allocentric rather than an egocentric frame of reference. Irrespective of their own distance from the dummy, the likelihood that the crabs rush back to defend their burrow increases strongly as the dummy approaches the burrow. In addition, the mean dummy–burrow distance at which the crabs respond is constant and independent of the dummy's direction of approach. We propose that to solve this sophisticated task of relative distance judgement, the crabs combine visual information on dummy position and direction with information on burrow location acquired during path integration2. In doing so, the crabs, like humans3, make clever use of the visual geometry of their environment.

This is a preview of subscription content, access via your institution

Access options

Buy this article

Prices may be subject to local taxes which are calculated during checkout

Figure 1: Two examples of a fiddler crab (Uca vomeris) responding with burrow defence to an approaching crab dummy.
Figure 2: The crabs' response probability (%) depends on the dummy–burrow distance.
Figure 3: The timing of the burrow defence response.
Figure 4: The probability of response for four length-matched segments around the closest point (Cp) of the dummy track to the crab's burrow (see inset).
Figure 5: The effect of the crab–burrow distance on the mapping of concentric circles around the burrow onto the ommatidial array of a fiddler crab eye13,14.

Similar content being viewed by others


  1. Collett, T. S. & Harkness, L. I. K. Analysis of Visual behaviour (eds Ingle, D. J., Goodale, M. A. & Mansfield, R. J. W.) 111–176 (MIT Press, Cambridge, MA, 1982)

    Google Scholar 

  2. Zeil, J. Homing in fiddler crabs (Uca lactea annulipes and Uca vomeris, Ocypodidae). J. Comp. Physiol. A 183, 367–377 (1998)

    Article  Google Scholar 

  3. Ooi, T. L., Wu, B. & He, Z. J. J. Distance determined by the angular declination below the horizon. Nature 414, 197–200 (2001)

    Article  ADS  CAS  Google Scholar 

  4. Crane, J. Fiddler Crabs of the World (Ocypodidae: genus Uca) (Princeton Univ. Press, Princeton, NJ, 1975)

    Google Scholar 

  5. Hyatt, G. W. & Salmon, M. Combat in the fiddler crabs Uca pugilator and U. pugnax: a quantitative analysis. Behaviour 65, 182–211 (1978)

    Article  Google Scholar 

  6. Jennions, M. D. & Backwell, P. R. Y. Residency and size affect fight duration and outcome in the fiddler crab Uca annulipes. Biol. J. Linn. Soc. 57, 293–306 (1996)

    Google Scholar 

  7. Montaque, C. L. A natural history of temperate western Atlantic fiddler crabs (Genus Uca) with reference to their impact on the salt marsh. Contrib. Mar. Sci. 23, 25–55 (1980)

    Google Scholar 

  8. Zeil, J. & Layne, J. Crustacean Experimental Systems in Neurobiology (ed. Wiese, K.) 227–247 (Springer, Heidelberg, 2002)

    Book  Google Scholar 

  9. Zeil, J., Nalbach, G. & Nalbach, H.-O. Eyes, eye stalks, and the visual world of semi-terrestrial crabs. J. Comp. Physiol. A 159, 801–811 (1986)

    Article  Google Scholar 

  10. Krapp, H. G., Hengstenberg, B. & Hengstenberg, R. Dendritic structure and receptive-field organization of optic flow processing interneurons in the fly. J. Neurophysiol. 79, 1902–1917 (1998)

    Article  CAS  Google Scholar 

  11. Wehner, R. ‘Matched filters’—neural models of the external world. J. Comp. Physiol. A 161, 511–531 (1987)

    Article  Google Scholar 

  12. Schall, R. Estimation in generalized linear models with random effects. Biometrika 78, 719–727 (1991)

    Article  Google Scholar 

  13. Zeil, J. & Al-Mutairi, M. M. The variation of resolution and of ommatidial dimensions in the eyes of the fiddler crab Uca lactea annulipes (Ocypodidae, Brachyura, Decapoda). J. Exp. Biol. 199, 1569–1577 (1996)

    CAS  PubMed  Google Scholar 

  14. Land, M. & Layne, J. The visual control of behaviour in fiddler crabs I. Resolution, thresholds and the role of the horizon. J. Comp. Physiol. A 177, 81–90 (1995)

    Article  Google Scholar 

Download references


We thank P. Dixon, L. Trott and L. Howlett for help; J. Wood for advice; and M. R. Ibbotson and M. V. Srinivasan for comments on the manuscript. The work was supported by a postdoctoral fellowship from the Swiss National Foundation to J.M.H. and in part by an Human Frontier Science Program (HFSP) grant.

Author information

Authors and Affiliations


Corresponding author

Correspondence to Jan M. Hemmi.

Ethics declarations

Competing interests

The authors declare that they have no competing financial interests.

Rights and permissions

Reprints and permissions

About this article

Cite this article

Hemmi, J., Zeil, J. Robust judgement of inter-object distance by an arthropod. Nature 421, 160–163 (2003).

Download citation

  • Received:

  • Accepted:

  • Issue Date:

  • DOI:

This article is cited by


By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.


Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing