Collective Locust Swarm
Behaviour and the
Environment
• When environmental conditions are favorable locusts
breed rapidly greatly increasing their population
numbers
• They first form bands as nymphs and then after 5
molts as adults they can form Swarms
• These swarms have been known to cover hundreds of
square miles and contain up to a billion locusts
• The collective behaviour of swarming in locusts is
largely affected by
1. The Landscape
2. Favorable environmental conditions (Rain, Temp)
3. Availability of Food which is all related to the
survival of the young
The Effects of Landscape
• Desert locusts Schistocerca gregaria outbreaks consistently start in
the same place according to historical records which suggests that
certain landscapes particularly favour outbreaks.
• High resource abundance promotes locust multiplication and the
contraction of resources into small patches increase concentration.
The effects of ecology
• High nitrogen levels: a faster
development, higher survival,
reproduced more and earlier
and also showed a greater
synchronization which is key to
the collective swarming
behaviour.
• Low Nitrogen Levels: active
and passive cannibalism but
this was not found in those that
were fed with the higher
nitrogen level leaves.
• Overall, this shows that the
nitrogen content of the host
plants in the landscapes that
the locusts dominate affect the
potential for population
increase
The effect of nitrogen
Sequence of Rainfall
• Spur throated Locust:
• Adults lay eggs in early wet
season:
>40mm rainfall needed for
oviposition
Another >40mm rainfall needed
for survival
• D. M. Hunter (1999):
populations increase more
than 50% when receive intial
and two or more follow up
rain intervals of less than 6
weeks
• Bullen (1969) showed that many
of the plagues between 1935 and
1968 began in year where there
was above average rainfall
following drought
“Locust swarms are spectacular and damaging
manifestations of animal collective movement”
J. Buhl et al. (2011)
Shapes, Dynamics and
Behaviour
• Types of swarm:
I. Columnar
II. Frontal structures
Australian Plague
Locust (Chortoicetes
terminifera)
Desert Locust
(Schistocerca gregaria)
Rhammacocerus
schistocercoides
Frontal structures:
• Highest concentration of locusts at the front
• Exponential decay of density as one moves towards the back
• Front forms a thin crescent shape where densities can reach several
thousand individuals per square metre and the rest of the group behind
this are scattered.
High Density Effects
Temperature Affects Density
Alignment 13.5cm
• Less than 13.5cm showed high proportion of individuals were moving in the
same direction
• Greater or equal to 13.5cm showed range of differences in polarity
The influence of spatial scales, Collett et al
1998
• Local spatial concentration of resources induces
gregarization
• Uneven resource distribution – crowding – increased
gregarization
• Positive feedback for behavioural change
• Mean contact threshold for gregarization in locally
concentrated habitats
Collective motion and cannibalism in locust
migratory bands (Bazazi et al 2006)
• Cannibalistic interactions influence Mormon
cricket migrations – general principle?
A) Abdominal denervation
• decreased detection of individuals from
behind
• Decreased probability of starting to move
• Decreased proportion of mean number of
moving individuals
• Increased cannibalism
• No influence on behaviour of isolated locusts
Mean proportion of moving locusts comparison of sham-operated controls and
denervated individuals
b) Restricted visual fields using black paint.
Lower proportion of moving locusts in back-blind compared to
front-blind individuals
• Within groups, abdominal biting and sight of
others approaching from behind triggers
movement
• Autocatalytic feedback - > directed mass
migration
• Balance between minimising your own risk from
cannibalism and allowing attacks of others
Questions?