Social behaviour, in which animals live in communities and work together, is well-known in the insect world, from bees and wasps to ants and termites. But it’s very rare in other groups of invertebrates.
However in 2005 scientists in Brazil found one pseudoscorpion – a miniature member of the arachnid group that includes spiders – was unusually social.
Not only that, in a unique twist they observed that a mother pseudoscorpion will sacrifice her life for the good of her offspring.
A BBC film crew has now captured this behaviour in extraordinary detail.
Pseudoscorpions look like tiny scorpions but without the stinging tail. They are still venomous to their prey, but their venom is carried on their claws instead.
They are abundant across the world, with over 3,000 species and 27 in the UK alone, but because they are so small – a matter of millimetres – and live their lives hidden away, they are little known or understood.
Their habitats are widespread and include leaf litter and decaying vegetation, mainly inside dead tree trunks; under stones; in caves and other similar environments.
The species that scientists studied in Brazil (Paratemnoides nidificator), makes its home in narrow spaces between the bark and the trunk of a tree. A colony contains as many as 175 pseudoscorpions.
They spin silken chambers in which they lay eggs and raise their young. The mothers then tend their offspring and bring them food.
Pseudoscorpions that live solitary lives tend to hunt prey smaller than themselves. But for the Brazilian species, the great advantage of being social is that they can hunt together, and catch bigger prey.
When on the hunt, these pseudoscorpions find a crack or edge in the bark. They hide just below the edge, but stick their pincers out into the open air. Then they wait.
They are acutely sensitive to vibration and can feel the approach of an insect such as a bee or an ant.
One pseudoscorpion will make a grab for the prey, gripping a leg or an antenna. Others will then rush up to grab it and they all inject their venom to immobilise it. Then they drag the body down under the bark, to feed to their young.
However when times are bad, food is scarce and the young are getting dangerously hungry, a mother pseudoscorpion has an unusual trick up her sleeve to keep them alive.
She will approach her youngsters and stand with her pincers held apart, gently vibrating. This is a signal to her young. She is saying: “I cannot catch any food, so eat me instead.”
Her young respond by doing exactly that. They surround her, stick their mouthparts into the joints of her legs and body, where her exoskeleton is thinnest, then they suck her dry.
This meal may prove a life-saver, tiding them over until food is more abundant and the other colony members can provide the next meal.
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