Species:

Habitat: Massive spider webs in southern Africa

It takes a lot to be a good aunt if you’re a . In fact, it takes your internal organs. After tending lovingly to your sisters’ eggs and regurgitating food for newborns, it’s time to offer yourself as the main course for the spiderlings to suck you dry.

“[The] spiders literally start feeding on the female while she is alive,” says at Aarhus University in Denmark. The spiderlings inject enzymes to dissolve her innards and suck out the semi-digested fluids, leaving only the outer shell. “But there is no apparent aggression. It looks as if females are almost inviting spiderlings to feed on them.”

S. dumicola are social spiders that live in large communal nests. Hundreds cooperate to capture prey, defend the nest and take care of the young. The nest is a dense retreat of silk and plant material, with two-dimensional webs to catch prey. Each spider only lives for a year, so can only reproduce once.

In the closely related species S. lineatus, only mated females care for spiderlings. In these spiders, the act of mating seems to cause females to care for other offspring as well as their own – an act called “alloparenting”. However, there are limits: they only let their own spiderlings eat them. Letting your kids eat you is a surprisingly common behaviour known as “matriphagy”.

Eat me!

Bilde and her colleagues wanted to find out whether unmated S. dumicola females also perform alloparenting duties. They bred spiders in the lab and placed them in groups, each with two mated and three virgin females, along with some spiderlings, to observe their behaviour.

Both virgin and mated females performed all forms of alloparenting. They tended to egg sacs, regurgitated food for spiderlings and finally offered themselves up as a meal.

This extreme behaviour makes sense because the spiders in a nest are all closely related and share genes. There are many more females than males, and only certain females reproduce, so the spiders in a colony are genetically similar.

“The investment in these offspring is an investment in her lifetime reproductive success,” says Bilde. “The more gene copies she propagates to the next generation, the better, so providing your body as food is a sensible evolutionary solution.”

“I suspect that females merely aren’t capable of discriminating between their egg cases and someone else’s,” says at the University of California, Santa Barbara. “The colony is composed of close kin, so even if females produced their own egg cases, there would still be a benefit of assisting a closely related relative.”

The spiders’ environment may also be a factor. “Spiders in the genus Stegodyphus occupy arid landscapes, deserts, where prey is mostly scarce,” says at the Israel Cohen Institute for Biological Control. A female who sacrifices herself will be “providing more food than they can find by foraging for prey”.

Journal reference: Animal Behaviour, DOI:

A simple meal is all that’s needed to determine the fate of a honeybee larva. It turns out that fragments of genetic material from flowers in their food control the bees’ destinies.

When female larvae are fed royal jelly, which is secreted by other bees, they develop into large-bodied, fertile queens. But most larvae eat beebread, a mixture of pollen and nectar. These larvae develop into smaller, sterile worker bees.

Xi Chen at Nanjing University in China and colleagues have now found that beebread contains lots of small RNA molecules called microRNAs. These regulate the expression of genes, and in plants they help regulate essential processes like making leaves and flowers.

“Plants utilise certain miRNAs to influence the size, morphology, colour and development of flowers,” says Chen. “Such characteristics of flowers guide [honeybees] in pollen collection.” As a result, a lot of these miRNAs end up in beebread, where larvae eat them.

Controlled by plant RNA

The researchers collected pollen, honey, royal jelly and beebread from hives and measured their miRNA levels. They found that beebread and pollen had much higher concentrations of plant miRNAs than royal jelly.

The team then reared bee larvae in the laboratory, feeding them a beebread mimic — a lab diet enriched with the same miRNAs as in pollen, at the same amounts. Larvae grown with miRNAs ended up as worker bees, with reduced weight and size, and smaller ovaries.

A closer look at the miRNAs in beebread suggested that the 16 most abundant could bind to 96 bee genes, some of which are known to affect development. One was amTOR, a gene known to be more active in queens. Further experiments showed that an miRNA called miR162a inhibits the function of amTOR.

However, when bee larvae were given only miR162a it didn’t prolong development time. This indicates that miR162a isn’t the only miRNA involved.

None of these effects were seen with royal jelly. “Queen-destined larvae [are] exempted from [miRNA] regulation,” says Chen.

Power of plants

But why should miRNAs from plants affect development in an entirely different species?

The authors point out that honeybees and flowering plants benefit from a long-standing “coevolutionary relationship”. The plant miRNAs could be part of that.

“When honeybees gather pollen as food for the entire colony, they pollinate plants; meanwhile, plants donate miRNAs to stabilise the honeybee colony,” Chen says.

Not everyone agrees with this interpretation, however. “I don’t think the plant is benefited by being involved in mechanisms that control insect development,” says at the University of Arizona in Tucson. “The simplest interpretation for me is that the miRNA is involved in signalling diet quality. It affects amTOR, which is also involved in the insulin signalling pathway.”

Tight grip

Elastic properties

A species of vulture has been filmed putting on make-up for the first time – a rare phenomenon in birds, known as cosmetic colouration.

The Egyptian vulture normally has a yellow wrinkled face surrounded by a halo of white hair. But on Fuerteventura island in the Canaries off the coast of Africa, many vultures sport reddish heads and necks, with the colour varying from pale brown to deep crimson.

These vultures dip their heads in red soil and swipe from side to side, carefully dyeing their head, neck and chest red. It is a well-studied population, so almost every vulture on the island is marked with plastic rings, allowing researchers to study individual differences in this curious behaviour.

“It’s the first documentation of this behaviour in wild birds that are individually marked,” says of Doñana Biological Station in Spain.

To see it up-close, Overveld and his colleagues kept two bowls in the island’s feeding station, one filled with red soil dissolved in water, the other with just water. As the hidden researchers watched, the vultures took their mud baths.

The birds examined the muddy water, scratched about with their legs, and then gently swiped both sides of their heads in the mud, emerging with red head, neck and chest feathers. Out of about 90 birds that visited over one day, 18 took mud baths. A couple of vain individuals even had two baths.

Something special

“The most interesting part of our observation is that there is great variation among individuals in the extent to which they paint feathers, ranging from almost completely white to almost completely red,” says Overveld.

The vultures did not follow a particular pattern while mud painting and the baths were not restricted to a particular age, or sex.

Although the related is known to display a similar behaviour as a signal of dominance, the researchers don’t believe that Egyptian vultures paint themselves for this reason.

Unlike the Egyptian vultures in the Canaries, the bearded vulture goes for its mud baths in secret, and the mud daubing itself is a lot more elaborate. Also, the bearded vulture is solitary, and the authors say signalling dominance may be more important for them.

So why do the Egyptian vultures do it?

One possible explanation is that the mud keeps bacteria and viruses away. But, if bathing had such a big advantage, many more birds should be taking long mud baths.

The authors believe instead that the painting serves a visual rather than health-related purpose, “given the great effect on the general appearance of these otherwise white birds.”

from Queen’s University in Ontario, Canada, thinks so too. “The amount and incidence of reddish head plumage on Egyptian vultures is quite rare, suggesting that those who have it are indicating something special,” he says.

But it remains to be seen what that function might be.

Some other to change the way they look. Many, , secrete waxy substances that they apply on feathers while preening to give them a glossy sheen.

Birds using dyes from their environment to change the way they look is rarer. Examples include that apply soil on themselves as camouflage when nesting, and close to the Arctic, when snow melts, perfectly camouflaged become suddenly conspicuous, and start applying mud as camouflage.

Winning combination

Species: The collector sea urchin (Tripneustes gratilla) – also called the cake or Parson’s hat sea urchin

Habitat: Coral reefs, seagrass meadows and algae forests in the tropical seas of the Indo-Pacific

The collector sea urchin looks like a pretty pincushion lying on the ocean floor, going about its business of munching on algae and seaweed.

But when threatened, this sedate pincushion has a most extraordinary defence. It releases a cloud of semiautonomous weapons: hundreds of tiny jaws that are still capable of biting and releasing venom even when separated from the sea urchin’s body.

Sea urchins have a hard, chalky shell covered in long spikes. Nestled among the spikes are tubular stalks topped with biting jaws known as pedicellariae.  One type of these appendages even has venom as well.

“The globiferous pedicellariae are minute and terrifying,” says at Southern Cross University in New South Wales, Australia.

The three-jawed, pincer-like heads bite attacking predators, releasing venom as they do so. They can get torn from the sea urchin but stay attached to the predator.

“When they were first observed, they were thought to be parasites, as they give the appearance of independent action from the main animal,” says Sheppard-Brennand.

Defensive cloud

In sea urchins, the pedicellarie usually remain attached to the body unless ripped off. But when the collector sea urchin is attacked, it releases the biting heads, forming a defensive cloud in the water around it, Sheppard-Brennand’s team has shown.

It can take 40 to 50 days for the pedicellariae to regenerate. But the urchins have a high density of these appendages and use only a small proportion of them per attack, says Sheppard-Brennand.

When the team simulated fish attacks in the lab by gently poking the urchins, they usually responded by releasing tens of the appendages. Individuals can emit hundreds in just 30 seconds, says Sheppard-Brennand.

Fish given food that contained pedicellariae rejected it, both in the lab and in experiments in the field. The venom seems to be crucial: when it was removed by soaking the pedicellariae in alcohol, there was far less of a deterrent effect.

Journal reference: The American Naturalist, DOI:

Species: São Tomé grosbeak (Crithagra concolor)

Habitat: Endemic to the rainforests of São Tomé island, Gulf of Guinea, West Africa

Deep within the rainforests of São Tomé, an odd-looking bird with burnished brown feathers and a grey, outsized, parrot-like beak lives in the canopy, making occasional forays into the world below for a fruit snack.

The setting – inaccessible forest on a small volcanic island that is one of the wettest places on Earth – only increases the mystique around this bird, which is one of the least observed of them all.

Now it turns out the species was also misidentified, and it is actually the largest canary on the planet, 50 per cent heavier than the next largest species.

Although it is small for a bird, being only about 20 cm long, the size of a common or European starling, the canary is a giant compared with other members of its genus, which are slightly smaller than house sparrows. It is found only on São Tomé and is critically endangered.

In 1888, Francisco Newton, a Portuguese naturalist, collected the first three specimens. The bird then vanished from popular record until 101 years later, when a couple of birdwatchers chanced upon it.

Its size, strange flattened head and large beak caused confusion among ornithologists. As a result, it was placed in a separate genus, Neospiza, which simply means “new finch”.

Over many years of fieldwork on the island, from the University of Porto, Portugal, collected four new specimens. Genetic analysis now shows beyond doubt that the grosbeak is a canary (genus Crithagra). Its closest relative is a seedeater, Crithagra rufobrunnea, that is found on São Tomé and the neighbouring island of Príncipe.

Accordingly, Neospiza concolor has been renamed Crithagra concolor.

The island of giants

The two Crithagra species diverged from a common ancestor about 1 million years ago. “Probably the grosbeak was already slightly larger and selection favoured the increase in bill size, allowing it to explore resources that are inaccessible to the smaller Crithagra rufobrunnea,” says Melo.

Very little is known about the natural history of this enigmatic bird. “Such a large bill is certainly linked to its diet, probably to deal with one or a few specific food items,” says Melo.

There are more than 140 bird species on SĂŁo TomĂ© and PrĂ­ncipe. Of these, 20 are endemic, including three giants – the grosbeak, a sunbird and a weaver bird, all of which are the largest in their respective families – and one dwarf, the smallest of the world’s ibis species. The island’s only native mammal species is also tiny: an endangered and elusive SĂŁo TomĂ© shrew.

“It is an interesting phenomenon that islands can cause bird taxa to become much bigger, but also much smaller than the species from which they derive,” says Nigel Collar of conservation partnership BirdLife International. “I think it has to do with adaptations to local environments in the absence of other competitors or in the presence of particular resources not found on the mainland.”

Read more: Smallest perching bird’s long-lost family revealed by genetics; Minimals: Meet the smallest critters of all; Biggest ever flying bird and the beast that dwarfed it

Species: A hoverfly, Toxomerus basalis

Habitat: On the sticky leaves of sundew plants in Brazil

Legless criminals

Kleptobugs

Octopuses have been recorded gathering up armfuls of debris – and remember, they have eight arms – before taking pot shots at one another. Whether it’s a case of “get off my turf” or merely “oops, didn’t mean to hit you” is still a puzzle.

Octopuses have siphons on the side of their body, which they normally use for jet propulsion – they expel water forcefully through them, shooting forward as a result.

Gloomy octopuses (Octopus tetricus) living on a bed of shells at Jervis Bay, Australia, seem to have co-opted this system to throw things at each other in what may be the first use of projectile weapons seen in octopuses.

“Very few animals have been reported to throw things at one another, so it would be significant if the octopuses are doing it”, says , a professor of philosophy at the Graduate Center, City University of New York, who presented video evidence at the in Cairns, Australia, this month.

Enthusiastic housekeeping

The technique the gloomy octopus uses seems to be a throw helped with a spit (see video above).

“In the ‘throwing’ behaviour, it gathers up a pile of stuff in its arms, and then directs the jet under the web of its arms, and throws out all the stuff under pressure,” says Godfrey-Smith. “So it’s a throw rather than a spit, though the throw uses water pressure – it uses a sort of inverted jet propulsion.”

Godfrey-Smith is not yet certain that the behaviour is intentional. It may just be a case of enthusiastic housekeeping showering the neighbours with debris.

“Octopuses often clean out their homes with a jet of water, pushing out sand and rubble. They also jet at intruders like pesky fishes,” says , a behavioural ecologist from the University of Lethbridge in Alberta, Canada, who was not involved in the study.

However, other octopuses were hit with the debris more often than you would expect by chance.

Eight-armed boxing

If indeed it is intentional, it may have evolved as a response to unusually crowded conditions at Jervis Bay.

The octopuses live on a midden made of shells, where they excavate dens. But with each octopus only having an area around a meter square to themselves, their neighbours can be as close as 30 centimetres away.

This is not the ideal living arrangement for solitary octopuses. But they probably put up with it because of overabundance of scallops – their favourite food – and a lack of other suitable nesting sites.

Even without the throwing behaviour, the crowding has brought out the worst in the inhabitants, it seems. A large female-male pair was caught on camera, for example, fighting intermittently for almost 2.5 minutes. Another time, a large octopus bullied a smaller one into leaving its den.

The team also observed many , where two octopuses probed rapidly at each other with their arms (Marine and Freshwater Behaviour and Physiology, DOI: 10.1080/10236244.2012.727617).

We are ready to do your bidding, all-powerful caterpillar (Image: Masaru Hojo)

Kill, Fido! Docile ants become aggressive guard dogs after a secret signal from their caterpillar overlord. The idea turns on its head the assumption that the two species exchange favours in an even-handed relationship.

The caterpillars of the Japanese oakblue butterfly (Narathura japonica) grow up wrapped inside leaves on oak trees. To protect themselves against predators like spiders and wasps, they attract ant bodyguards, Pristomyrmex punctatus, with an offering of sugar droplets.

The relationships was thought to be a fair exchange of services in which both parties benefit. But from Kobe University in Japan noticed something peculiar: the caterpillars were always attended by the same ant individuals.

“It also seemed that the ants never moved away or returned to their nests,” he says. They seemed to abandon searching for food, and were just standing around guarding the caterpillar.

Flipping the tentacle

Intrigued, Hojo and his colleagues conducted lab experiments in which they allowed some ants to interact with the caterpillars and feed on the secretions, and kept others separate.

Ants that ate the caterpillar’s secretions remained close to the caterpillar. They didn’t return to their nest.

And whenever the caterpillar everted its tentacles – flipped them so they turned inside out – the ants moved around rapidly, acting aggressively.

In the field, Hojo saw the ants attack predatory spiders and wasps, so he thinks the caterpillar responds to predators by ordering ant servants to attack them.

“There are glandular cells near the tentacles that could be secreting chemical signals,” says Hojo. “It is possible that both visual and chemical signals are stimulating the ant aggression.”

Doped up

Back in the lab, ants that had not eaten caterpillar secretions did not react when the tentacles flipped.

So it seems that caterpillars can directly dictate the behaviour of ants, and it’s something in their sugary secretions that makes the ants such obedient servants.

The team found that doped up ants had lower levels of dopamine, a compound shown to affect movement and aggression in insects, than ants that had not eaten the secretions.

To investigate further, the team treated the ants with a drug called reserpine that blocks the transport of dopamine.

Ants that previously reacted to the tentacle eversion by becoming more aggressive, stopped doing so, suggesting that dopamine does indeed play a role.

The chemical cocktail in the caterpillar secretion that affects dopamine levels in the ants is yet to be identified.

Unequal partners?

These findings hint that the ant-caterpillar mutualism, which is similar to relationships found between many other species, could actually be a manipulative parasitic behaviour.

“This is really perspective-changing”, says from the Indian Institute of Science Education and Research in Pune. “I’d like to see how it may work across other species hitherto believed to be mutualistic.”

The situation isn’t so clear cut, says of the Center for Research and Advanced Studies of the National Polytechnic Institute in Irapuato, Mexico.

“The benefit for the caterpillar is obvious, but we do not know whether the benefit for the ants is as minimal as the authors argue,” he says. “If the liquid that the caterpillars secrete is sufficiently nutritious, then it might well be that the overall balance for the ants also is positive.”

Journal reference: