By Jennifer Welsh, LiveScience Staff Writer
LiveScience.com – Tue, Jun 12, 2012


After leaving its detachable penis
to finish inseminating the female, the male orb-web spider fights to
the death to protect the impregnated gal. Without the extra weight of
its sexual organs, this spider can outlast its competition, new research
has found.

Though the spider loses its palp (the arachnid equivalent of a penis,
and the male orb-web spider has two), it usually wins the fight to
protect his mate from other males.

"Prior work has demonstrated that eunuch spiders
are superior fighters, we here pinpoint a mechanism that enables
eunuch's greater endurance," the researchers write in their paper,
published June 13 in the journal Biology Letters. "Our present results
imply that palp weight poses significant physical costs to males."

Risky sex

Several types of male spiders and other insects engage in risky sex, which, in the orb-web spider Nephilengys malabarensis, ends in about 75 percent of them being eaten by the female. But, even if they escape their mate's grasp, they lose one or both of their palps along the way.

The broken-off organ efficiently plugs the female's genital opening,
making sure other males can't fertilize her; a study reported in January
that these detached palps continue to pump sperm into the female.
Sometimes only one of her two openings, called the epigynum, gets
plugged, meaning there's room for another male to squeeze in and
inseminate her. [The Weirdest Animal Penises]

If they survive the female's cannibalism, the male spiders stay nearby,
guarding her from other males that might try to dislodge the plap plug
and inseminate their female. Interestingly, these eunuch males usually
win fights with other, intact, males.

Detachable penis

The researchers wondered if there were any other benefits


to leaving the palp behind in the female. So, they took male orb-web
spiders and amputated none, one or both of their palps, then ran them
around the lab until they were exhausted (when they wouldn't move after
five nudges with a paintbrush).

Removing one palp reduced the spider's
body weight by 4 percent, removing both reduced their weight by 9
percent. In turn, their endurance increased 32 percent in half-eunuchs
and 80 percent in full eunuchs. This supports what the researchers
called a "gloves-off" mating strategy. The spiders have nothing to live
for other than protecting their potential offspring. They are able to
fend off other males because they are lighter in weight after
dispensing their palps.

"Increased endurance probably enables eunuchs to perform better in the
contests with intact rivals," the authors write. "Mating biology of N. malabarensis males consists of a plethora of mate-guarding
and male–male agonistic behaviors that are physically demanding; an
elevated endurance will hence put eunuchs at an advantage over intact
rivals."

The study will be published tomorrow (June 13) in the journal Biology Letters.

Follow Jennifer Welsh on Twitter @microbelover or LiveScience @livescience. We're also on Facebook & Google+.



I woke up this morning with a bad hangover
And my penis was missing again.
This happens all the time.
It's detachable.

[background singing begins: "detachable penis" over and over]

This comes in handy a lot of the time.
I can leave it home, when I think it's gonna get me in trouble,
or I can rent it out, when I don't need it.
But now and then I go to a party, get drunk,
and the next morning I can't for the life of me
remember what I did with it.
First I looked around my apartment, and I couldn't find it.
So I called up the place where the party was,
they hadn't seen it either.
I asked them to check the medicine cabinet
'cause for some reason I leave it there sometimes
But not this time.
So I told them if it pops up to let me know.
I called a few people who were at the party,
but they were no help either.
I was starting to get desperate.
I really don't like being without my penis for too long.
It makes me feel like less of a man,
and I really hate having to sit down every time I take a leak.
After a few hours of searching the house,
and calling everyone I could think of,
I was starting to get very depressed,
so I went to the Kiev, and ate breakfast.
Then, as I walked down Second Avenue towards St. Mark's Place,
where all those people sell used books and other junk on the street,
I saw my penis lying on a blanket
next to a broken toaster oven.
Some guy was selling it.
I had to buy it off him.
He wanted twenty-two bucks, but I talked him down to seventeen.
I took it home, washed it off,
and put it back on. I was happy again. Complete.
People sometimes tell me I should get it permanently attached,
but I don't know.
Even though sometimes it's a pain in the ass,
I like having a detachable penis.

[background voices continue to sing "detachable penis" for
a while, then out]