I've been working on a number of projects
investigating the behavioral and ecological mechanisms
underlying migratory band formation and movement in the
Mormon cricket, Anabrus simplex (Tettigoniidae).
Mormon crickets can form huge migratory bands in the
western U.S. consisting of millions of individuals that
travel en masse up to 2 km/day and can devastate
agricultural areas (see photo above). Despite the obvious
similarities between migratory bands of Mormon crickets and
those of locusts, my laboratory work on Mormon cricket
behavior demonstrated that the behavioral mechanisms
underlying band formation and movement are quite different
in the two groups (Sword, 2005).
In collaboration with Pat Lorch (Kent State university)
and Darryl Gwynne (University of Toronto,
Mississauga), we have been using radiotelemetry, GPS,
and GIS to examine the landscape-scale movement
patterns of individual Mormon crickets within
migratory bands. To date, we have tested hypotheses
about differences between the movement patterns of
individuals in outbreak and non-outbreak populations
(Lorch et al. 2005), and also examined the effects of
various environmental and social cues on migratory
band movement patterns.
We recently performed a manipulative experiment
demonstrating for the first time that Mormon crickets and
locusts form migratory bands as part of an anti-predator
strategy (Sword et al., 2005). However, once these groups
form, individuals in the group must contend with increased
competition for resources as well as the threat
cannibalism. In a really neat set of experiments conducted
this past summer with Steve Simpson (University of
Sydney) and Iain Couzin (Princeton/Oxford), we
demonstrated that Mormon crickets in migratory bands
move for two reasons: 1) to exploit new nutritional
resources, namely protein and salt, and 2) to avoid
being eaten by hungry conspecifics approaching from
the rear (Simpson et al. 2006). These findings
provided a unique demonstration of the nutritional
basis of mass movement and a novel perspective on the
mechanisms underlying collective animal movement
patterns. In short, Mormon cricket migratory band
movement is a forced march driven by cannibalism.
Run!!!
As an analog to the phylogenetic analysis of swarming in
Schistocerca locusts, I am completing a
mtDNA-based phylogeographic analysis of Mormon crickets
throughout their range in western North America. This will
provide a phylogenetic framework upon which to examine
population-level variation in migratory behavior and its
relationship to environmental factors such as the insects'
nutritional environment. This study also facilitated the
discovery of a cryptic species of Anabrus in
Washington state, USA identified through variation in
cytochrome oxidase (COIII) mtDNA sequence data (Sword et
al. in preparation).
Relevant Publications
Simpson, S.J.*, Sword, G.A.*, Lorch, P.D.
& Couzin, I.D. (2006) Cannibal crickets on a forced
march for protein and salt. Proceedings of the National
Academy of Science USA 103:4152-4156. (* equal
contributors)
Sword, G.A. (2005) Local population
density and the activation of movement in migratory
band-forming Mormon crickets. Animal Behaviour
69(2):437-444.
