SPIDERS EAT IS A BIG SURPRISE
predator can set a trap to catch bats and snakes, grab fish from lakes
and supplement this carnivorous diet by eating plant material? Considering
this wide-ranging assortment of prey, plus the fact that this voracious
group of hunters have been documented to make their predatory attacks
on every continent except Antarctica, should we be worried that humans
might also be on the menu? Not likely, because the animals are spiders,
and the largest ones in the world get no bigger than our hands.
I was once
again appreciative of what a diverse world we live in when I received
an unusual request from Martin Nyffeler, senior lecturer in zoology
at the University of Basel in Switzerland. He sent me some photos of
snakes to identify.
I see hundreds of cell phone photos people send in wanting identification
of snakes and other animals. But these snake photos were different.
most were snakes from regions from which I do not typically get requests:
Taiwan, India, Malaysia and Australia. But the truly bizarre feature
was that each was a small snake that had been entangled in a spider
web and then consumed by the spider. I did the best I could in helping
him with the snake identifications, turning to colleagues in other countries
for confirmation of a couple of them.
In my communications
with Nyffeler, I found out that he has published several scientific
papers on spider diets. I was intrigued. Among the more fascinating
of his publications about what spiders eat were ones on bats, fish and
of a fish-eating spider in the Southeast and once saw one that had caught
a small mosquitofish. But I had no idea that fish predation by spiders
is a global phenomenon.
a dozen species of spiders have been documented to engage in capturing
fish, with a total of 89 observed incidents.
strategy is for the spider to sit alongside shore, stretch out its front
legs, and when a fish swims by, to ambush it.
most spiders eat insects that are smaller than they are, the average
size of fish eaten is more than twice the length of the spider itself.
The documented size record for a fish caught by a spider is a goldfish
3.5 inches long.
fishing spiders of the Amazon are suspected of catching even bigger
fish, but with little likelihood of anyone observing the operation.
high on the surprise meter for me, as well as other ecologists, was
Nyffeler's scientific review paper on bat-catching spiders. Incidents
of spiders preying on bats have been primarily ones where a bat was
caught in a web before the spider proceeded to kill and eat it.
have fangs and venom, so they come well-equipped for the job. As is
often true in science, some biological phenomena are not recognized
as being widespread, even common, until someone does a scientific review
of the literature, much of which may be anecdotal.
observations that are mentioned incidentally in books or scientific
papers are often not recognized as being the norm rather than the exception
until someone accumulates the records. Such is the case with bats in
which more than 50 accounts of spiders eating bats were confirmed.
have traditionally considered spiders to be active carnivores or scavengers.
However, ecologically significant, although less dramatic than predator-prey
accounts, are 95 compiled records of 60 species of spiders eating plants.
as exciting as a spider ensnaring a bat or snake or pouncing on a fish
but a clear indication that ecologists still have much to learn about
the intricate interactions among plants and animals.
documentation of the dietary versatility of spiders is a real eye-opener.
Let's be thankful that spiders don't get as big as horses or we would
surely find ourselves on their list of preferred prey.
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