Turning into a monster

Turning into a monster

So what is it that turns this harmless solitary herbivore into part of an unstoppable cloud that consumes all that is in its path?

 

Well it all starts with a bit of rain followed by some nice weather that improves conditions in just the right way for the locust that then go onto reproduce at high numbers. How does this lead to these otherwise docile creatures turning into a swarm of ravenous monsters?

As their population size increase the levels of the locust change to suit the high densities by becoming more mobile but also more hungry…..

So what changes occur between the two types of locusts?

Physical

The brain of a gregarious locust grows to be about 30% large than a solitary locust, this helps the locust change their behaviour to suite a more generalist diet, where they need to remember what plants are best to consume over others. The larger brain will also help with the behavioural requirements needed to be part of a swarm such as having the ability to recognise the behaviours of other members of the swarm to reduce the effects of intraspecific competition. There is also a reduction in overall body size to allow the locust to be more mobile by reducing energy cost of having a larger body as well as an increased metabolism to help with the greater increase in energy output used by continuously moving over large distances.      

 Social/feeding

Solitary locusts do not occur in high densities and tend to move away from other locust they come in contact with each other.  whereas the gregarious locusts will swarm together in densities of more than  100 locusts m² and at these densities they will switch from eating a small range of host plants which become less available, too consuming a large range of plants unspecific plants that they come across as they travel across the land.

How do these locusts know that it’s time to swarm?

When the locusts come into close contact with each other they brush against hairs on their hind legs that trigger the release of serotonin this then compels the locusts to keep together as it gives them a chemical reward for being in close quarters with each other.  

Once the locust are together they start to march in columns that can be up to 6km long, they will continue this marching through the nymph stages of their life cycle but once they reach fall development they will fly in massive swarms that can cover large areas and eat everything they can that crosses their path until the population becomes too unstable to support as the resources start to deplete the locust can become cannibalistic as they need to feed constantly to support their high metabolisms.

These swarms are unpredictable as there is still a lot that isn’t know about them, there is also variation within the species of locust that can produces these swarms thus adding more complexity to what we need to know to understand the swarming behaviour that they exhibit and how to control them, so they do not cause millions of dollar of damage in the areas in which they occur .

 so until there is a time where we can control them people will always have to eyes to the skies and listen for the buzz of the swarm.

 

reference:

Ott SR, Rogers SM. 2010. Gregarious desert locusts have substantially larger brains with altered proportions compared with the solitarious phase. Proceedings of the Royal Society B-Biological Sciences 277(1697):3087-3096.

Simpson SJ, Despland E, Hagele BF, Dodgson T. 2001. Gregarious behavior in desert locusts is evoked by touching their back legs. Proceedings of the National Academy of Sciences of the United States of America 98(7):3895-3897.