Spiders astound scientists by suckling young

Scientists say the arachnid gives babies sustenance four times as nutritious as anything a cow can offer

A species of spider is rewriting natural history after scientists discovered it produces milk and suckles its young for nearly 40 days. Until now, lactation has been considered a purely mammalian trait, but researchers have recorded the ant-mimicking jumping spider feeding on milk.

SPIDERS are not noted for their maternal bonding – some spiderlings even devour their mothers shortly after hatching.

But the ant-mimicking jumping spider is rewriting natural history after scientists discovered it produces milk and suckles its young for nearly 40 days.

Much like baby mammals nursing at the teats of their mothers, researchers have recorded the tiny spiders gathering to feed on super-nutritious milk produced in an opening from which the eggs are released.

Until now, lactation has been considered a purely mammalian trait. Although some non-mammals such as pigeons, flamingos, emperor penguins and cockroaches produce a similar nutritious fluid, it is considered fundamentally different to milk.

But researchers at the Chinese Academy of Sciences in Beijing said the fluid secreted by the spiders was four times as nutritious as cow’s milk, and could be considered as true milk.

They found that feeding continues long after the little arachnids can forage on their own and probably evolved during a period when food was scarce.

Writing in the journal Science, author Dr Rui-chang Quan, said: “Extended parental care could have evolved in invertebrates as a response to complex and harsh living environments that require offspring skills to be fully developed before complete independence. The mother’s physiology, behaviour, and cognition might have changed to adapt to providing milk and prolonged maternal care as in mammals. The discoveries presented in this study will encourage a re-evaluation of the evolution of lactation and its occurrence across the animal kingdom.”

Scientists studied the ant-mimicking jumping spider because of its strange living arrangements in which adult females cohabit with juveniles when most other young have left the nest.

The researchers speculated that the teenagers were hanging around because they were still receiving care and food from their mother.

After following the spiderlings from hatching, the scientists noticed that for at least 20 days neither mother nor babies left the nest, yet the offspring continued to grow as if they were being fed, more than trebling in size in the period. Closer observations revealed that the mother provided a seemingly nutritious fluid from her underside. Although spiderlings left the nest to forage from about 20 days, milk suckling continued until they reached the subadult stage at around 40 days when no more milk was produced.

Unlike cockroaches, which deposit a nourishing fluid to the brood sac of the growing embryos, the spiders use a specialised organ and continue to suckle their young over an extended period, like mammals.

The researchers believe the milk might be made from unfertilised or failed eggs which are reused to feed the newly emerged offspring.

When they blocked up the duct producing the milk, all the spiders died within 10 days, but when allowed to flow 76 per cent made it to adulthood.

In other species, such as the wolf spider, only one per cent survive.