Spider cannibalism

Male Spiders Let Mates Eat Them for Kids' Sake

The unkind act of butchering and eating your mate after sex, typified by the female black-widow spider and praying mantis, may make for healthier babies, new research suggests.

The researchers found that a male orb-web spider makes the ultimate evolutionary sacrifice: giving his life for the health of his offspring.

Sexual cannibalism is the act of one partner eating the other after sex. In the orb-web spider Argiope bruennichi, the female tries to grab and wrap up the male at the onset of mating so she can snack on him during sex. In the lab, only about 30 percent of the males survive their first mating, but by letting the female gnaw on them, the males prolong the sex act, making it more likely they will inseminate their partner.

Of these survivors, half go on to find a second mate, while the others try again for the same female. Due to the male's anatomy, two copulations is the limit. (When you are facing a life without sex, is it really worth it to go on?)

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Polar bear 'cannibalism' pictured

By Jonathan Amos
Science correspondent, BBC News, San Francisco

It is an image that is sure to shock many people.

An adult polar bear is seen dragging the body of a cub that it has just killed across the Arctic sea ice.

Polar bears normally hunt seals but if these are not available, the big predators will seek out other sources of food - even their own kind.

The picture was taken by environmental photojournalist Jenny Ross in Olgastretet, a stretch of water in the Svalbard archipelago.

"This type of intraspecific predation has always occurred to some extent," she told BBC News.

"However, there are increasing numbers of observations of it occurring, particularly on land where polar bears are trapped ashore, completely food-deprived for extended periods of time due to the loss of sea ice as a result of climate change."

The journalist was relating the story behind her pictures here at the 2011 American Geophysical Union (AGU) Fall Meeting, the largest annual gathering of Earth scientists.

A paper describing the kill event in July 2010 has just been published in the journal Arctic. It is co-authored with Dr Ian Stirling, a polar bear biologist from Environment Canada.

Ross had approached the adult in a boat. She could see through her telephoto lens that the animal had a meal, but it was only when she got up close that she realised it was a juvenile bear.

The kill method used by the adult was exactly the same as polar bears use on seals - sharp bites to the head.

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