Bizarre Tremex behavior??

Bill Shear wshear at EMAIL.HSC.EDU
Wed Sep 4 15:48:05 CDT 2002

On 9/4/02 3:06 PM, "Ken Kinman" <kinman at HOTMAIL.COM> wrote:

> Bill,
>    Yes, at least one specimen was collected (removed from the horse's
> hide).  This was by a concerned horse-owner (in Canada) who posted a
> photograph to, and both I and a professional
> entomologist (from Florida) agree that it is Tremex (or something very
> close).  To me it looks like Tremex columba, but perhaps there are other
> species which look similar.
>     The Canadian who collected it thought that the wasp was sucking blood
> from the horses, but it is clearly an ovipositor.  I suppose blood would get
> into the ovipositor in the process.
>     Anyway, I have not yet been able to find any literature on horntail
> wasps (Siricidae) trying to "oviposit" their eggs into a horse (or any other
> animal, for that matter).  I find this interesting, trying to figure out why
> such drastic "host-switching" (animals instead of trees) would occur.  Lacks
> of appropriate trees?  Pesticides or genetic defect affecting the brain of
> the wasp (i.e., "mistakes" a horse for a tree).
>     If this occurrence is scientifically documented (it was posted by a
> concerned horse-owner, not a scientist), I guess there could be a number of
> reasons that this might occur-----especially these days as mankind continues
> to disrupt natural ecologies in so many different ways.  Or perhaps this
> does occur naturally if a horse rubs up against a tree and thus "smells"
> right to the mother wasp.  I can only speculate, but this is just so odd
> that it really caught my attention.

Before going to the more elaborate hypotheses--it may be that ovoposition
was not in fact taking place.  Perhaps the wasps were obtaining some
resource from the horses, akin to the phenomenon of "puddling" in many
Lepidoptera, where the insects gather around damp mud or places where
animals have urinated to obtain the nitrogen and/or minerals in which their
diet of nectar is lacking.  Is it possible the insects were lapping up horse
sweat, rich in sodium?  And clinging tightly with their legs, so as to
simulate the attachement that may be attributed to the ovipositor?

The horse might "smell" right to the wasp if wood shavings were used as
bedding and the horses were in the habit of rolling in the bedding.

Here's a story that might serve as an example.  Many years ago, a local
newspaper reporter I knew asked me to look at a situation his neighbor had
reported.  On a hot summer day, while the neighbor was out doing errands,
his dog was murdered by swarms of honeybees.  The dog was dead, evidently of
convulsions, and thousands of bees littered the dogyard.  What would have
caused this?  Of course, one hypothesis might have been that the dog and the
bees were driven mad by man's disruption of the environment, or by

However, I reasoned as follows:  It was a hot day, and bees cool their combs
by collecting water to spread over them.  The dog was chained up near a
large basin of water.  Perhaps bees were visiting the basin.  When the dog
came over to drink, they might naturally have "buzzed" him.  Dogs
instinctively snap at insects flying near them, and in perhaps crushing or
killing some bees, he released alarm pheromone.  This would trigger stinging
in the other bees, releasing further pheromone, attracting more bees.  Had
he not been chained, the dog could have run away, but as it was, he had to
stay in the dogyard and be stung by ever-increasing numbers of bees--at
least 2000, estimating from the dead bees round about (honeybees are
eviscerated by stinging and soon die).  The overload of venom caused caused
a hyperallergic reaction which killed the dog.  The whole incident could be
explained in terms of instincts normally highly functional, but in this
particular set of circumstances, lethal for all concerned.

Hypotheses non fingo est, as someone once said!

Bill Shear

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