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he might get eaten before he ever gets a chance to
mate,” says Scott.
And the dangers of a male’s mating quest extend
beyond hungry partners. “Lots of things eat spiders,”
says Scott, including birds, wasps, ants and other
spiders. Exactly what eats them at her field site on the
Pacific coast is unclear — it’s rare to witness actual
predation — but more than 80 percent die during their
searches for females.
Besides not wanting to be eaten, males have another
incentive to traverse risky terrain as fast as they can,
vying for first place in the beach race: If he’s the first to
mate with a female, he can block off her reproductive
tract, thus thwarting mating attempts by rivals.
Understanding how this works requires some
spider sex ed. “Black widow spider genitalia are
ridiculous and amazing,” says Scott, referring to a
male’s bizarre sperm transfer organs. Unconnected
to his gonads, these two “pedipalps” stick
out like bulbous boxing gloves in front of
his face. When ready to mate, he deposits
his sperm-containing fluid onto a special
web, then uses his pedipalps to suck it up.
Both sexes have pedipalps, but only the
male’s function like turkey basters.
If a female consents and copulation
occurs, the pedipalp’s corkscrew-shaped
tip breaks off inside her reproduc-
tive tract, forming a plug. Placed well,
that plug prevents additional males
from mating with her.
WEB WARS
Males can pull another sneaky stunt that could stack
the paternity odds in their favor. After arriving at a
female’s web (provided she doesn’t eat him), males
begin cutting out pieces, bundling them up with their
own silk. Until recently, it wasn’t clear why they did this.
Scott designed an experiment, which appeared in
Animal Behaviour in 2015, to see what these males were
up to. At Island View Beach and Cordova Spit, where
the Tsawout First Nation allows Scott land access for
her work, every square yard of driftwood-covered
sand hosts two to three adult females. There, Scott and
her colleagues set up cages along the beach to test how
males would respond to intact versus altered webs.
Some cages had no webs in them at all. These were
the controls, to see how many males would randomly
stumble across them. In the rest of the cages, the
researchers allowed females to build webs, then
removed the spiders.
The researchers left some of these caged webs
untouched. They placed males inside others, and gave
them an hour to make alterations before taking them
back out. In still others, the researchers snipped the
webs themselves, with scissors. After all the different
cages were set up on the beach, the ecologists counted
how many wild males living nearby showed up in
sticky traps beside each treatment.
Scott found the intact and human-snipped webs
were equally attractive to males. But the webs that
male spiders had altered attracted significantly fewer
rivals — a third as many as the other webs. This sug-
gests that this odd dismantling and bundling behavior
seems to reduce how attractive a female’s web is to the
competition.
Not all widow spider scientists think these radi-
cal web renovations constitute
sabotage, though. Yael Lubin, a
professor emeritus at Ben-Gurion
University of the Negev in Israel,
has a different take. “I regard [web
reduction] as part of the courtship
behavior, but the function is still
under discussion,” she says.
Scott also suspects that van-
dalism is not the only purpose of
this web cutting and bundling. It’s
likely part of the overall chemical
conversation, she says, noting that
males have sex pheromones, too.
THE TOOLS OF SEDUCTION
While the function of the male-female web interplay
is still debated, the potency of female pheromones is
unquestioned. Lubin, who has studied spiders since
NOTES FROM EARTH
Catherine Scott
(above) keeps an eye
on a female western
black widow spider.
Scott counts male
spiders in traps (top)
at her research site,
where she’s studying
how attracted males
are to experimentally
altered female webs.A male black widow
will use pedipalps, odd
sperm-transfer organs,
to mate with a female.
He finds his lady’s web
via the pheromones
she emits.