What Gall! The Crazy Cribs of Parasitic Wasps | Deep Look

Plenty of animals build
their homes in oak trees, but it’s another thing
entirely to get the oak tree to do all the work. To build your house for you. Say you’re an oak tree,
just sitting there minding your own business, when suddenly
this tiny wasp comes along. She says hey, why
don’t you build me a nursery for these baby
wasps I’m about to have? And then she injects her
eggs under your skin. You find yourself creating an
entirely new structure, one you would have never
built for yourself. What nerve, you
might say, what gall! And you’d be right. This thing, this parasitic
wasp house, it’s called a gall. There can be dozens of types
of galls on a single tree, each one built to order for
a specific species of wasp. They’re called
gall-inducing wasps, and each gall is weirder and
more flamboyant than the next. Sometimes the wasps
prefer a mobile home. This one is called
a jumping gall. It falls from the
tree and bounces across the ground like
a Mexican jumping bean until it finds a
safe place to hatch. As a protection
against predators, galls can taste
incredibly bitter, bitter like the bile produced
by a gallbladder. In fact, the earliest doctors
believed being bitter and angry meant an excess of
gall in the body. Anyway, back to our tree. Inside the gall, the
larvae mature and develop, and as they grow they
release chemicals that tell the tree
how to build the gall. The tree is tricked
into funneling nutrients into the gall to feed
the hungry wasp larvae. Scientists call this
a physiologic sink. For the larvae, it’s like
living inside a giant banana, an endless supply of food. But the peace and
quiet don’t last long. All that free food starts
attracting uninvited guests. That original wasp
itself becomes a host for another set of
wasps, called parasitoids. One study in the UK found
17 different wasp species living in one gall. But the oak tree? It does just fine, in most cases
unharmed by the tiny rivalries in tiny houses on its
branches and its leaves.

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