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Self-Interest

Much of economics and ethics rests on the idea of maximizing utility, or satisfaction of people's interests. This raises the question of what is in a person's interest. For instance, is it in the interest of a male spider to mate with a female if doing so will lead to his death?

In many species of insects and spiders, females eat their partners after sex.
Such cannibalism clearly brings advantage to the female, who gets an easy snack. But the benefits (if any) for the male are less obvious. ...
Dr Schwartz and Dr Hebets note that, after mating, the males of one species of arachnid, the dark fishing spider, spontaneously die and thus ensure that they get eaten. This is in contradistinction to the behaviour of most male spiders, who usually attempt at least some sort of a getaway, even if it is futile.
- Sexual cannibalism in spiders: Male dark fishing spiders sacrifice themselves for the good of their offspring, Economist, Oct. 22, 2016



Although both fertilized and unfertilized eggs are probably eaten by thousands of species, the practice of consuming eggs from the same species has led to an interesting take on the “kids meal.” So-called trophic eggs, produced by some types of spiders, lady beetles and snails, function solely as food and often greatly outnumber the fertilized eggs in a given clutch.

But the black lace-weaver spider (Amaurobius ferox) takes the concept of prepackaged meals a step further. One day after spiderlings hatch, new mothers lay a clutch of trophic eggs, which are doled out to their hungry babies. This keeps them satisfied for the next three days, after which the spiderlings are ready for their next stage of development.

After their first molt, black lace-weaver spiderlings are too large for their mother to care for, though they are in dire need of additional food. In a sacrificial act of parenting, she calls the babies to her by drumming on the web and presses her body down into the gathering crowd.

The ravenous spiderlings swarm over their mother’s body. Then they eat her alive.
- BILL SCHUTT, In Many Species, a Family Dinner Means Something Else, NYT, JAN. 30, 2017


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