Do Spiders Make Milk?
WouterThe question “do spiders make milk?” has been posed. Scientists have long assumed that mammals are the only animals that produce milk. However, there are a number of invertebrates, including some insects and cockroaches, that produce milk-like fluids.
Researchers studied the behavior of jumping spiders, a common species of arachnid that is native to southeast Asia. They discovered that the mothers would provide young with milk for the first 20 days of their lives. These milk-like fluids have four times the protein content of cow’s milk, and are fat-rich.
After this time, the youngsters are allowed to forage. But they still return to the mother’s nest to nurse. This extended parental care is a behavior attributed to long-lived social vertebrates. It’s likely that the spiders had developed this trait in response to food shortages and harsh living conditions.
Researchers say that the jump spider is one of the few arachnids known to provide milk to its offspring. Unlike many invertebrates, it has no mammary glands, but instead uses its own organs to regurgitate pre-digested food for its young.
As with mammals, the spiderlings drink from tiny droplets of milk-like fluid left by the mother on the nest. The quality of the milk depends on the mother’s diet. Spiderlings receive five milligrams of fat, two milligrams of sugar, and 124 milligrams of protein per milliliter.
However, researchers aren’t sure how the females produce milk. They think it may come from unfertilized eggs.
