The most important feature of mammals as land-based animal dominators is their complex body structure, which can be used to secrete milk through the breast, which is breastfeeding. However, scientists have recently discovered that in some spider species, breastfeeding behavior also occurs. In addition to overthrowing some traditional zoological classification concepts, because mothers breastfeeding means that their young children cannot feed themselves, is this species evolution or degradation?
This has caused global media attention and became the world's first new discovery from a laboratory in Yunnan Province, China. In 2017, Chinese ecologist Chen Zhanqi observed in the laboratory's artificial spider nest that young spiders would attach to their mothers, just as mammalian babies sucked on their mother's nipples.
This spider species, called Toxeus Magnus, is also known as the giant ant spider. Originally in a park in Singapore, Chen Zhanqi found that in his spider's nest, there were adult female spiders about a few centimeters in size, surrounded by several young juvenile spiders. The situation is unusual because most spider species are accustomed to living alone, and even the behavior of cannibalism, only a few spiders have social skills. Toxeus Magnus is not the exception. It belongs to the family of the spider family and is known for its own foraging.
However, as far as observations are concerned, they live in a family group, and mothers take care of their newborn children like mammals. Chen Zhanqi brought a few spiders back to the country and noticed that the female spiders will give birth to 2 to 36 spider eggs at a time, while the primary spiders will not leave the nest spontaneously after hatching, but will stay in the nest at least 3 weeks. They never left during the period and the mother never brought food back outside. However, the size of the newborn spider will grow four times during the time, and the only source of nutrients is the mother's milk.
When the spider eggs hatch, the female spiders begin to make tiny milky liquids around the spider's nest. The young spiders will suck the lotions around the nest at first, and after a few days, they will line up to suck on the mother's body. Under the microscope, if the female spider's abdomen is squeezed, some white water droplets will ooze out and quickly turn yellow in the air. When the team analyzed the fluids, it found that it contained protein, fat, and sugar like milk, and the protein ratio was four times higher than that of regular milk.
Chen Zhanqi and Quan Ruichang, who are engaged in biological research at the Tropical Botanical Garden of the Chinese Academy of Sciences, recently published their observations in the academic journal Science, confirming that the mother of the jumping spider, Toxeus Magnus, did conduct a breastfeeding behavior. Their offspring produce milk, and even if the spider is adult, the behavior will continue.
Chen Zhanqi mentioned that if the mother's milk supply is cut off during the period, all spiders that have grown for less than 20 days will die. If the mother is removed from the nest, the spider will grow at a slower rate and leave the nest earlier, more likely to die before adulthood.
Of course, spiders are arthropods, and there is no breast in the body structure. It is rare to breastfeed. Among the insects and other invertebrates, the habit of breastfeeding by the mother and long-term care of the child is almost unheard of. Quan Ruichang said that these "spider milk" itself is a liquefied egg that flows out of the birth canal prematurely. He pointed out that some amphibians and other invertebrates also have the ability to let their offspring eat similar substances to provide nutrition.
As pointed out by Rosemary Gillespie, an evolutionary ecologist at the University of California at Berkeley, other spider species provide similar feeding practices for their offspring. In a study conducted in 1990, a spider named Coelotes was found that would allow their children to eat some sediment on the spider web. Another spider called Amaurobius, the mother will give birth to the oocysts, and the oocysts will immediately be swallowed by the young spiders.
But whether spider milk is truly "milk" depends on how it is defined. Traditionally, for example, milk has been defined as a nutrient solution secreted by the breast, while the mammary gland is only present in mammals. But if the concept of breastfeeding is extended to any form, and parents use secretions to provide nutrition for young children, then some species of spiders on the earth do grow up with milk.
Although the discovery is not intended to study whether spider milk can one day replace milk or other processed dairy products, Nick Royle, a behavioral ecologist at the University of Exeter in the UK, points out that the findings help people understand complex parental relationships and evolution.
According to Royle, this pattern of behavior suggests that their offspring need more care from their parents. Young spiders do not have enough ability to get food, have the opportunity to be eaten by other carnivores before growing and breeding, so the mother becomes the main dependence of the young spider. He added that because the form of breastfeeding will place a heavy burden on the mother, these spider species are likely to develop in the extreme conditions.
Katie Hinde, a breastfeeding specialist at Arizona State University, said she is more interested in knowing whether these spider milks contain other ingredients such as hormones, immune chemicals, and bacteria in mammalian milk.
"These rare variants of the animal kingdom give us further insight into the changes in parental care." Hinde described all mammals as producing milk, but why do they do this? In the past, scientists had to use genetics or fossils to trace back to biological history and understand the reasons for the evolution of breeds. However, in the case of Toxeus Magnus, a non-mammalian that can produce milk, Hinde said: "We can observe what causes the parental rearing style to evolve on a large scale."
Hinde expects that the greatest contribution of this amazing discovery will encourage scientists to re-evaluate the evolution of mammals.