More than a few men have fought to the death to win a woman. Now it appears there's a biochemical force driving the duels—in squid, at least.

According to a new study, when male longfin squid touch recently laid eggs, the males rapidly shift from calm swimming to extremely aggressive fighting (see raw video above).

(Related: "Global Warming Making People More Aggressive?")

Researchers first noticed this effect while studying male squid arriving at breeding grounds where females had already started laying egg capsules.

Each egg capsule contains 150 to 200 eggs. A female squid will lay 20 to 30 capsules over a period of up to several weeks, during which time she will mate with multiple males, according to the National Oceanic and Atmospheric Administration.

The scientists noticed that, when male longfin squid saw egg capsules laid on the seafloor, the squid would swim toward the eggs and wrap their arms around them.

"This struck us as a very weird behavior," said study co-author Roger Hanlon, of the Marine Biological Laboratory in Woods Hole, Massachusetts. The team then saw that as soon as the squid contacted the capsules, the males became highly aggressive, violently beating and grappling with each other.

(Related: "Large, 'Glamorous' New Glowing Squid Species Found.")

Keen to take a closer look, Hanlon and colleagues presented 57 pairs of male squid with egg capsules and closely monitored their behavior in the lab.

Upon touching the capsules, the males attacked one another, even in the absence of females, the researchers found.