Vomiting caterpillars weigh up costs and benefits of group living

Apr 06, 2012
Vomiting caterpillars weigh up costs and benefits of group living
Many species of caterpillars defend themselves by regurgitating semi-digested food. Image by Dr Mike Speed

(PhysOrg.com) -- A type of caterpillar which defends itself by regurgitating on its predators is less likely to do so when in groups than when alone, a new study by researchers from the University of Bristol and the University of Liverpool has found. Such reluctance is sufficient to cancel out the benefits of being in a group.

The study, published today in , will help in the design of more sustainable methods for reducing crop losses caused by and similar pests.

have some remarkable and unusual ways to defend themselves against enemies.  While many rely on nasty stings and dangerous venoms, the caterpillars of the large white butterfly (Pieris brassicae) protect themselves by vomiting on their .

These caterpillars, like many other species that have anti-predator defences, live in groups so that they have safety in numbers.  However, many studies have shown that the size of a group does not affect the chance of survival in several different species.

Caterpillars of this species have reason to use their defensive regurgitation weapon sparingly since the loss of food through vomiting slows down growth, reduces survival and even reduces female reproduction by lowering the number of eggs.

This new study shows that there is a social side to defensive vomiting.  The researchers found that whether a caterpillar is willing to regurgitate – and to what extent – depends on the size of its social group.

Dr Andrew Higginson of Bristol’s School of Biological Sciences said: “Because defensive regurgitation is so costly, each individual does better if one of its siblings is the one to vomit to deter the predator.  Therefore, some individuals appear willing to risk being ‘cheats’, not investing in the costly defence, and exploiting the likelihood that other individuals will defend instead.  Crucially we found that the number of non-vomiting individuals increased as their risk decreased with group size – a result of safety in numbers.”

Co-author, Dr Mike Speed of Liverpool’s Institute of Integrative Biology continued: “Caterpillars take account of their group size when ‘deciding’ whether to vomit because they are trying to avoid the cost of vomiting.  In a group, it is quite likely that the predator will taste other individuals as well, each of whom might vomit and cause the predator to give up and leave.  Also, caterpillars compete with each other for food, and so the bigger the group the more important it is to not vomit.”

Using a mathematical model, the researchers show that this reduced tendency to vomit can easily explain why the size of a group does not affect the chance of survival.

Dr Higginson added: “This study helps us to better understand the defences of many caterpillars and similar insects, several of whom are important crop .  It will ultimately help in the design of more sustainable methods for reducing experienced by farmers.”

Explore further: Dogs hear our words and how we say them

More information: ‘Density-dependent investment in costly anti-predator defences: an explanation for the weak survival benefit of group living’ by Derek Daly, A. D. Higginson, Dong Chen, G. D. Ruxton and M. P. Speed in Ecology Letters

Related Stories

Insects that deter predators produce fewer offspring

Jan 25, 2011

Scientists studied the defences used by caterpillars that transform into large white butterflies, called Pieris brassicae. The insects regurgitate semi-digested cabbage leaves to make them smell and taste unpleasant to predators. ...

Ladybirds - wolves in sheep's clothing

Jun 24, 2011

(PhysOrg.com) -- CSIRO research has revealed that the tremendous diversity of ladybird beetle species is linked to their ability to produce larvae which, with impunity, poach members of 'herds' of tiny, soft-bodied ...

Caterpillars aren't so bird brained after all

Apr 04, 2011

(PhysOrg.com) -- Caterpillars that masquerade as twigs to avoid becoming a bird's dinner are actually using clever behavioural strategies to outwit their predators, according to a new study.

Recommended for you

Dogs hear our words and how we say them

9 hours ago

When people hear another person talking to them, they respond not only to what is being said—those consonants and vowels strung together into words and sentences—but also to other features of that speech—the ...

Amazonian shrimps: An underwater world still unknown

10 hours ago

A study reveals how little we know about the Amazonian diversity. Aiming to resolve a scientific debate about the validity of two species of freshwater shrimp described in the first half of the last century, ...

Factors that drive sexual traits

11 hours ago

Many male animals have multiple displays and behaviours to attract females; and often the larger or greater the better.

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.