One of the traits setting mammals apart from other orders within the animal kingdom is the ability to secrete nutritious milk to feed their dependent offspring. A new study from the Chinese Academy of Sciences could change that outlook, however. It seems milk is not only for calves, kittens, puppies and human infants - it's also for spiderlings, at least those of the Toxeus magnus species. Those spiders, which are commonly known as jumping spiders, have been found to secrete a "nutritious milk-like substance," according to the study.
Much like mammals, this substance is critical for the spiderlings during their early stages of life. The study stated the behavior of the spiderlings is very similar to the behavior of mammals in those same stages of development. The milk from the mother spider is also part of the more advanced stages of the young spiders' lives. Many return to their mother to collect her secretions even after they reach sexual maturity - yet another trait formerly believed to exist only in mammals.
Those spiderlings get the secretions from their mother's abdomen. They wait for her to spread it across the surface of the nest for their first week of life. After that, they received it directly from their mother, much like piglets and puppies do. They reached maturity within 20 days, but would still continue to return to the nest they recently left to continue to collect from their mothers for as long as an additional 18 days.
After those 18 days, though, the mother was still letting her female progeny continue to come into her nest and feed, but males were attacked. The Chinese study stated this could be a method for the species to prevent inbreeding, as the young were now in the midst of sexual maturity.
The research also showed the spiderlings were just as dependent on their mothers' milk as mammals are on theirs. If the milk glands were removed or blocked, the young spiderlings died within 10 days. When the mother was taken from the nest at the 20-day mark in which the spiderlings matured enough to wander out of the nest and collect food on their own, the size of the spiders diminished, and so have their survival rates.
Spiders are not the only non-mammals to secrete for the nourishment of their young. Other creatures such as pigeons and cockroaches have similar methods of caring for their young. The results of this study, however, may lead scientists to reexamine the methods of nurture other species of spiders and invertebrates as a whole care for their young. They may be more caring than previously known.