Adult ants, praying mantises, guppies, rats, and apes occasionally eat their young, their siblings, or adults of the opposite sex. Some spiders, however, practice a rarer form of cannibalism: the young may eat their mother. Amaurobius ferox, a half-inch-long spider common in European woodlands, practices matriphagy. Within a week after the young hatch, according to entomologists Kil-Won Kim and Andre Horel, at Universite Henri Poincare in Nancy, France, the mother spider actively solicits them to kill and devour her. For three weeks in late spring and early summer, the mother spider sits in close contact with her egg sac until eighty to a hundred spiderlings emerge. She then lays a second batch of eggs, on which the young immediately feed. Three to four days later, the spiderlings molt. The next day, the mother increases her activity, drumming with her legs, jumping around, and pressing intermittently against the clustered brood. Within half an hour, they swarm over her body and begin to feed. Mothers never attempt to escape or fend off the fatal attacks. ("Matriphagy in the spider Amaurobius ferox: an example of mother-offspring interactions," Ethology 104, 1998)
COPYRIGHT 1999 American Museum of Natural History
Arachnophilia - baby Australian spiders eat their mother - Gruesome Diets II - Brief Article
Discover, Nov, 1995
THEODORE EVANS, A ZOOLOGIST AT the University of Melbourne, hadn't been studying the Australian social spider Diaea ergandros for long when he realized that the baby spiders ate their mothers. Aristotle had observed this charming behavior in other spiders more than 2,000 years ago, but until now no one had tried to explain it. "Why would you let your offspring eat you?" Evans wondered. "It seems so anti-Darwinian."
Cannibalism in the animal kingdom is usually a case of the large preying on the small and weak. Within a family it's generally the parents who weed out the runts and feed them to bigger, stronger siblings. Not only does the Australian spider's matriphagy stand this norm on its head, but, even more curious, it doesn't occur only under extreme circumstances--it's a natural part of the life cycle.
After a mother spider lays a clutch or 40 eggs, she cannot reproduce again. The babies hatch in midspring or early summer, safe inside a nest of eucalyptus leaves. During the warm summer months, the mother captures large insects up to ten times her own weight, much too big for her babies to finish. "It's a bit like a great big Christmas dinner," says Evans. "Everyone eats as much as possible, but there's always going to be a lot left over."
The mother fattens herself up on the leftovers, storing nutrients in unfertilized eggs in her ovaries. "She's like a living refrigerator," Evans explains. When the weather cools and insects become more scarce, nutrients from the eggs seep into the mother's bloodstream. As the spiderlings get hungrier, they raid the fridge--sucking nutrient-rich blood from their unresisting mother's leg joints. Evans compares the process to baby mammals drinking their mother's milk. But in this case, the babies literally suck their mothers dry. After several weeks the mother becomes so weak she can hardly move. At this point the spiderlings attack their mother just as they would prey, injecting her with venom and digestive juices and consuming her entirely.
Evans noticed that if the spiderlings finished eating their mother before the end of the fall, they resorted to eating one another. The longer a mother lasted, the more of her offspring survived. So it's Darwinian after all: in sacrificing her body, a mother who would not live to reproduce again ensures that more of her genes are passed on to the next generation, because her offspring do not eat one another. "Spiders are usually considered to be quite repugnant and horrible little creatures, but this is the ultimate form of parental care," says Evans. "This is TLC beyond the pale."
COPYRIGHT 1995 Discover
From http://spider.gilgamesh.de/index.htm, the home page of Dr. Jutta M. Schneider, Researcher of Behavioral Ecology of Spiders.
My research interests are the evolution of reproductive behaviour and sociality. I selected spiders as my main study objects because they show a huge variety of brood care and mating strategies. In addition, some spider species developed forms of group-living that are distinct from the better studied social insects.
My main research projects involve the adaptive significance and the mechanism of suicidal maternal care and its implications for group-life as well as sexual conflict in the spider genus Stegodyphus. More recently I have started to investigate the costs and benefits of sexual cannibalism in the genera Nephila and Argiope in collaboration with Prof. Mark Elgar at the University of Melbourne, Australia.
Below, I will briefly summarise some of my projects. For more information you may want to consult the publications or contact me.
SUICIDAL MATERNAL CARE Brood care in Stegodyphus lineatus always ends with the death of the mother. She first feeds the young with a liquid regurgitate and is finally sucked dry. In a field experiment we found that females retain their potential to lay eggs again but that predation pressure is so high that it does not pay to reduce current reproductive investment in favour of future reproductive investment. The best strategy is to put all available resources into the single brood so that the offspring will have a maximal body size at independence.
Stegodyphus spiders produce tiny eggs in comparison to other species of that size. Instead the young hatch premature and grow very quickly afterwards on their maternal diet. A selection pressure that may have favoured such a reproductive strategy over the alternative of larger eggs is that mortality of adult females is very high during the period of egg development. The shorter this period will be, the higher are the chances for a female to complete maternal care. The age specific mortality is due to a parasitic wasp that is specialised on adult female Stegodyphus. However, the larva of the wasp will not survive when there are spiderlings. Therefore, once the young have hatched, the mortality risk through the wasp is removed which caused 30% of the mortality in earlier stages.
Three species of the genus Stegodyphus are permanently social. It is unknown how they manage their brood care but it is clear that the adult females are consumed by young as is the case in other species. The question is whether all females feed all young and eventually allow matriphagy (killing the mother) or whether there exists a mechanism that prevents such an extreme form of cooperative care. Social spiders are notoriously difficult to breed in the laboratory making such a question difficult to answer. Observations in nature are also not possible because the brood care takes place inside a densely woven nest. Therefore, I studied the question in S. lineatus with a large set of foster experiments. It turns out that only females that are in the right developmental stage will feed young from other females. Females that are adult but unmated or have eggs will not care for foster young. If the social spiders have such a mechanism as well, communal matriphagy will be possible but only with those females that have young of their own. Females that initiated their reproduction later, will be safe to survive until their own young have hatched.
A poem inspired by Matriphagy
Location: Brooklyn, NY
by Richard Fein
A mirror is meaningless to the Amaurobius ferox
for her world within flows into the world without
like a fluid, and her existence
is the weakest eddy in time, a tiny whirlpool in the current.
She's always drowning with no past to recall
or lost future to regret,
the ultimate unexamined life,
but a life worth living.
She does what she does on her own woven silk,
calling forth her hungry spiderlings,
goading them by plucking silver strings,
playing her own dirge till her brood is roused
and a shroud of a hundred hides the devouring.
She who never really was, never dies--
But the spider is neither mother Mary nor Medea,
for mother nature casts her in the most primal play
compelling her to recite the script by rote,
in the barest outline of the scene.
A passionate reading is reserved
for the more difficult plays,
performed by hot-blooded actresses gazing into mirrors
and applying the appropriate make-up
for the maternal roles they choose to play