Scientists discover first-ever bee 'soldier'

Jan 09, 2012
Jatai forager bee (left) and the larger Jatai guard

(PhysOrg.com) -- University of Sussex scientists working with researchers in Brazil have identified the first example of a 'soldier' bee.

The discovery was made by a team of scientists from the University of Sussex and the University of Sao Paulo including Professor Francis Ratnieks and Dr Christoph Grueter, from the University of Sussex Laboratory of Apiculture and .

The team studied a common tropical stingless bee Tetragonisca angustula in Sao Paulo State in where it is known locally as Jataí. It nests in tree and wall cavities. Each nest has one queen and up to 10,000 workers.

Insect societies such as the Jataí’s are defined by cooperative and altruistic behaviour, with the workers caring for the nest and the queen’s offspring. This lifestyle also includes the division of labour among workers.

This video is not supported by your browser at this time.
Tetragonisca angustula entrance with standing and hovering guards

The research, published today in the journal Proceedings of the National Academy of Sciences (PNAS) states that:

-- Jataí guard bees are 30 per cent heavier than their forager nestmates;

-- they differ slightly in shape from foragers, with disproportionately larger legs and smaller heads;

-- approximately one per cent of workers bees reared in a colony are soldier-sized;

-- Jataí soldiers stand on the nest entrance tube and also hover near the entrance where they provide “early warning” detection of enemy attack

Like other social insects, Jataí use guard workers to protect the nest. A previous study by the team had shown that these guards were specialists who performed guarding duties for far longer (up to three weeks) than other types of worker bee, such as the honey bee, who spend just one day guarding the nest, progressing to other tasks as they get older. 

This video is not supported by your browser at this time.
Tetragonisca angustula guard fighting with Lestrimelitta limao.

The new research shows that Jataí guards, unlike their honey bee counterparts, are morphologically (physically) specialised to perform a particular task, being consistently larger than their nest mates.

Having larger-bodied guards is important for nest-defence, as they are better at fighting one of Jataí’s main enemies – the robber bee Lestrimelitta limao, which can kill off many colonies when raiding nests for food. These guards, then, are more like the ‘soldier’ workers found in some ant and termite colonies.

Jatai soldier bees guarding nest entrance and hovering nearby

Even though the Jataí guard lacks a sting and is eventually killed, it can clamp its head onto the wing of a robber bee, preventing it from flying.

The discovery is significant in terms of the evolution of advanced insect societies. Large-bodied soldier workers have long been known in ants and termites, but this is the first evidence of a bee – a worker physically designed for active defence of the .

Professor Ratnieks says: “Stingless bees are not defenceless. Jataí is one of the most common found in Brazil, but its sophisticated defences make it one of the most amazing.”

Explore further: How rockstars and peacocks attract the ladies

More information: A morphologically specialised soldier caste improves colony defense in a neotropical eusocial bee, Grüter, C., Menezes, C., Imperatriz-Fonseca, V. L., Ratnieks, F. L. W.. Proceedings of the National Academy of Sciences (2012). doi:10.1073/pnas.1113398109

Abstract
Division of labor among workers is common in insect societies and is thought to be important in their ecological success. In most species, division of labor is based on age (temporal castes), but workers in some ants and termites show morphological specialization for particular tasks (physical castes). Large-headed soldier ants and termites are well-known examples of this specialization. However, until now there has been no equivalent example of physical worker subcastes in social bees or wasps. Here we provide evidence for a physical soldier subcaste in a bee. In the neotropical stingless bee Tetragonisca angustula, nest defense is performed by two groups of guards, one hovering near the nest entrance and the other standing on the wax entrance tube. We show that both types of guards are 30% heavier than foragers and of different shape; foragers have relatively larger heads, whereas guards have larger legs. Low variation within each subcaste results in negligible size overlap between guards and foragers, further indicating that they are distinct physical castes. In addition, workers that remove garbage from the nest are of intermediate size, suggesting that they might represent another unrecognized caste. Guards or soldiers are reared in low but sufficient numbers (1–2% of emerging workers), considering that <1% usually perform this task. When challenged by the obligate robber bee Lestrimelitta limao, an important natural enemy, larger workers were able to fight for longer before being defeated by the much larger robber. This discovery opens up opportunities for the comparative study of physical castes in social insects, including the question of why soldiers appear to be so much rarer in bees than in ants or termites.

Related Stories

Predator pressures maintain bees' social life

Dec 21, 2007

The complex organisation of some insect societies is thought to have developed to such a level that these animals can no longer survive on their own. Research published in the online open access journal BMC Ev ...

Male wasps help to defend the nest

Apr 27, 2011

Male wasps are not exactly famous for their contributions to domestic life. Most do precious little, leaving the nest's maintenance chores to the females. Now a group of researchers has shown that when push ...

Recommended for you

Bats use polarized light to navigate

33 minutes ago

Scientists have discovered that greater mouse-eared bats use polarisation patterns in the sky to navigate – the first mammal that's known to do this.

How fussy pandas maintain a balanced bamboo diet

4 hours ago

(Phys.org) —Pandas are famously fussy eaters, but new research suggests there is method to their madness, with the animals switching between different species and parts of bamboo plants to maintain a balanced ...

New planthopper species found in southern Spain

10 hours ago

Not much is known about the the genus of planthopper known as Conosimus, which now includes six species after a new one was recently discovered in the southern part of the Iberian Peninsula in the Spanish ...

How rockstars and peacocks attract the ladies

Jul 21, 2014

What is it that makes rockstars so attractive to the opposite sex? Turns out Charles Darwin had it pegged hundreds of years ago – and it has a lot to do with peacocks.

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

NTRandallD
not rated yet Jan 10, 2012
It is quite disingenuous to assign "altruistic" behavior to an insect. This smacks of anti-anthropomorphic reporting in which any species that exhibits sacrificial behavior is deemed superior to man and thus altruistic.