In spiders, size matters: Small males are more often meals

September 10, 2008
A female wolf spider, Hogna helluo, consuming a male. Credit: Shawn M. Wilder

Female spiders are voracious predators and consume a wide range of prey, which sometimes includes their mates. A number of hypotheses have been proposed for why females eat males before or after mating. Researchers Shawn Wilder and Ann Rypstra from Miami University in Ohio found, in a study published in the September issue of the American Naturalist, that the answer may be simpler than previously thought.

Males are more likely to be eaten if they are much smaller than females, which likely affects how easy they are to catch. In one species of spider, Hogna helluo, large males were never consumed while small males were consumed 80% of the time. This result was also confirmed when Wilder and Rypstra examined published data from a wide range of spider species. Males are more likely to be eaten in species where males are small relative to females.

Much research on sexual cannibalism has focused on a few extreme cases involving sexual selection and sperm competition. However, by looking at data on a wide range of spiders, Wilder and Rypstra discovered that the size of the male relative to the female (often referred to as sexual size dimorphism) determines how often sexual cannibalism occurs in a species.

"We were surprised to find that such a simple characteristic such as how small males are relative to females has such a large effect on the frequency of sexual cannibalism," states Shawn Wilder. In many cases, sexual cannibalism may not be a complex balancing act of costs and benefits for males and females but rather a case of a hungry female eating a male when he is small enough to catch.

In an interesting twist, evolution does not appear to be driving this relationship. For example, females would not become larger to consume more males because each male would then be a smaller meal to the larger female and males would not become smaller to be eaten more often because they would not get to mate as often. Rather, sexual cannibalism may be a byproduct of the evolution of large females and small males in a predatory species.

Shawn M. Wilder and Ann L. Rypstra, "Sexual size dimorphism predicts the frequency of sexual cannibalism within and among species of spiders" American Naturalist (2008) 172: 431

Source: University of Chicago

Explore further: Researcher explores male perceptions about HPV

Related Stories

Researcher explores male perceptions about HPV

November 29, 2016

Maggie Pitts took great interest in the human papillomavirus vaccine after Virginia became the first state in the country to mandate its use among girls in the sixth grade.

Recommended for you

Uncovering the secrets of water and ice as materials

December 7, 2016

Water is vital to life on Earth and its importance simply can't be overstated—it's also deeply rooted within our conscience that there's something extremely special about it. Yet, from a scientific point of view, much remains ...

Swiss unveil stratospheric solar plane

December 7, 2016

Just months after two Swiss pilots completed a historic round-the-world trip in a Sun-powered plane, another Swiss adventurer on Wednesday unveiled a solar plane aimed at reaching the stratosphere.

Giant radio flare of Cygnus X-3 detected by astronomers

December 7, 2016

(Phys.org)—Russian astronomers have recently observed a giant radio flare from a strong X-ray binary source known as Cygnus X-3 (Cyg X-3 for short). The flare occurred after more than five years of quiescence of this source. ...

Dark matter may be smoother than expected

December 7, 2016

Analysis of a giant new galaxy survey, made with ESO's VLT Survey Telescope in Chile, suggests that dark matter may be less dense and more smoothly distributed throughout space than previously thought. An international team ...

ANU invention to inspire new night-vision specs

December 7, 2016

Scientists at The Australian National University (ANU) have designed a nano crystal around 500 times smaller than a human hair that turns darkness into visible light and can be used to create light-weight night-vision glasses.

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.