Why Do Spiders Produce Milk?

One of the most unusual features of arachnids is the fact that spiders produce milk. It’s a strange concept, but it’s also the first time this has been reported in an invertebrate. Until now, milk production has only been observed in mammals, including humans.

In an experiment, scientists squeezed the abdomens of mother spiders. The result was a white droplet that oozed from the abdomen. They thought this might be milk, but it wasn’t.

Researchers then blocked the epigastric furrow with a Wite-Out. This prevented the mothers from excreting their milk.

As a result, the female jumping spiders couldn’t nurse any longer. They died. Their babies were also affected. A study found that, in the early days, baby spiders depended entirely on their mother’s milk.

While there are other animals that have been found to produce a milk-like fluid, such as pigeons and cockroaches, spiders are the first invertebrate to do so.

The milk produced by spiders is similar to cow’s milk, but it contains four times as much protein and fat. Other species of invertebrates, such as earwigs, have also been observed to produce milk-like secretions.

Scientists speculate that spiders may have developed this trait in response to a shortage of food or a harsh environment. There are other long-lived social vertebrates, such as elephants, that have been known to have extended lactation periods.

Though the researchers aren’t certain of whether the behaviour of spiders is unique or more similar to that of mammals, the behaviour appears to play a significant role in reproductive success.