The words ‘spider’ and ‘milk’ are not two that you’d generally expect to see in the same sentence. But that’s exactly what researchers at the Chinese Academy of Sciences in Yunnan have found: a spider mother feeding her offspring with her own milk.
The behaviour was seen in a species of ant-mimicking jumping spider found in Taiwan called Toxeus magnus. The researchers first made the discovery after noticing a baby spider hanging onto its mother in the lab, in a way that reminded them of a baby mammal.
Mothers producing milk for babies is usually behaviour confined to mammals, but some bird species can produce something known as ‘crop milk’ and use it to feed their young. The intensive parental behaviour seen in these spiders, however, is rare.
Female spiders of the species lay up to 36 eggs at one time. The researchers noticed that when the baby spiders first hatched, they sipped ‘milk’ that their mother had deposited in droplets around their nest. But before long, they began lining up to drink the milk straight from their mother’s egg-laying tract, and they kept on doing this until they were 40 days old, well after they were old enough to forage for food themselves.
To test what they were seeing, the researchers painted the mother spider to stop the milk reaching her offspring. After they did this, spiders that were younger than 20 days old all died. When the mother was removed from the nest, older spiders grew more slowly and were less likely to survive to adulthood, suggesting the milk was giving them a significant advantage.