The European sand flea or sand-hopper, Talitrus saltator (Montagu, 1808) is an amphipod crustacean (Family Talitridae; Order Amphipoda) which lives on sandy shores from Norway to the Mediterranean. Most people have probably seen them hopping about on the beach, especially in the zone of wet sand created as waves go out or the tide falls. Their typical habitat is the so-called eulittoral zone which lies between the spring high and low tide lines. They remain buried in the sand or under seaweed during the day, emerging at night to forage for food, particularly as the tide falls. They are opportunistic omnivores – can eat anything – and play an important role in the decomposition of organic matter on beaches. They vary in size, up to a maximum of about 1.5 cm (0.6 inch) long.
When photographing these little amphipods on a beach in Spain, I noticed that when disturbed from their place of shelter under a piece of seaweed, they hopped about madly then suddenly stopped and remained dead still, lying in the sand. In fact, this was the only way to photograph them since they are so tiny and jump about so quickly that it is virtually impossible to capture them in motion. Funnily enough, despite looking at a number of research papers on their biology, I could find very few, if any references to this behaviour. The only mention I could find, of suddenly going stiff, or ceasing to move (‘playing possum’), was an aside in an old science book by J. Arthur Thomson (7). This behaviour may be an adaptation to avoid detection by wading birds (?), or it could just be a prelude to them burrowing into the sand.
Talitrids have an amazing ability to remain within their optimal zone, the moist sand at the seashore (Borgioli et al., 1999). If a sand-hopper is moved from its burrow to dry conditions, it runs or hops seawards; whilst conversely, if they are immersed in seawater or placed on overly wet substrate, they crawl or hop up the beach in a landward direction! (Scapini et al., 1996) This ability to place themselves back in their favoured position is called ‘zonal recovery’. They do not return to the exact same burrow if they are moved, but nevertheless actively recover to the zone they prefer to burrow in. They have to do this because they rely on gills to uptake oxygen, so they need wet sandy conditions. Thus, they try to avoid both dry sand, and being buffeted around by waves further down the beach. The smaller juvenile sand-hoppers – which are unable to burrow – are active closer to the water’s edge.
To place themselves in their optimal zone, sand-hoppers use a variety of behavioural cues, including sun compass navigation, an awareness of the landscape and micro-climatic conditions such as humidity. The sun compass navigation in T. saltator appears to be based on the rate of angular displacement of the azimuth (angle of the sun) rather than the movement of the sun per se (Scapini et al., 2002).
These little creatures live for a surprisingly long time: up to 21 months in the case of the males, who live longer than the females. They are not exactly threatened, but seem to thrive better on undisturbed beaches where human impact is minimal (Barca‐Bravo et al., 2008).
These photographs were taken on 16th Sept 2017 on Esterio Beach near O Barqueiro, Galicia, Spain.
- Scapini, F. E., Fallaci, M. A. & Mezzetti, M. C.(1996). Orientation and migration in Talitrus saltator. Revista Chilena de Historia Natural, 69, 553-563.
- Fanini, L., Marchetti, G. M., Scapini, F., & Defeo, O. (2007). Abundance and orientation responses of the sandhopper Talitrus saltator to beach nourishment and groynes building at San Rossore natural park, Tuscany, Italy. Marine Biology, 152(5), 1169-1179.
- Borgioli, C., Marchetti, G. M., & Scapini, F. (1999). Variation in zonal recovery in four Talitrus saltator populations from different coastlines: a comparison of orientation in the field and in an experimental arena. Behavioral Ecology and Sociobiology, 45(2), 79-85.
- Barca‐Bravo, S., Servia, M. J., Cobo, F., & Gonzalez, M. A. (2008). The effect of human use of sandy beaches on developmental stability of Talitrus saltator (Montagu, 1808)(Crustacea, Amphipoda). A study on fluctuating asymmetry. Marine Ecology, 29(s1), 91-98.
- Scapini, F., Rossano, C., Marchetti, G. M., & Morgan, E. (2005). The role of the biological clock in the sun compass orientation of free-running individuals of Talitrus saltator. Animal Behaviour, 69(4), 835-843.
- Scapini, F., Aloia, A., Bouslama, M. F., Chelazzi, L., Colombini, I., ElGtari, M., … & Marchetti, G. M. (2002). Multiple regression analysis of the sources of variation in orientation of two sympatric sandhoppers, Talitrus saltator and Talorchestia brito, from an exposed Mediterranean beach. Behavioral Ecology and Sociobiology, 51(5), 403-414.
- Thomson, J. A. (1922). The Outline of Science, Fourth Volume. Wildside Press LLC.