According to this website of a team of researchers:
Responses of Invertebrate Herbivores to Stinging Trichomes of Urtica
dioica and Laportea canadensis
Tracey D. Tuberville, Peter G. Dudley, A. Joseph Pollard
Oikos, Vol. 75, No. 1 (Feb., 1996), pp. 83-88
doi:10.2307/3546324
This article consists of 6 page(s).
They hypothesized that Urtica evolved more as a response to mammals
than to insects.
But I do not see how Urtica can penetrate the thick hides of most
grazing animals. I doubt that
stinging nettle would penetrate deer or buffalo.
As for mice and rodents, they would not do enough damage to the plant
to bother with.
So that leaves insects such as swarms of grasshoppers.
So I would have my bets not on mammals but insects and especially
grasshoppers.
Unless the stinging nettle works on the mouth and tongue of a mammal.
For humans it
would be the skin, since we are not eating nettle. So maybe it is the
mouth and tongue
of mammals that the nettle is targeting.
And then, of course, the evolution of the nettle was to ward off all
herbivores be they
mammals or insects.
Maybe the chemicals involved tell us who the targeted victims are?
Some say histamine
and acetocholine and folic acid are involved. So does anyone know if
these chemicals
target the mouth of a mammal or the mouth of a insect?
Perhaps the toxic chemicals involved tell us which mammals and insects
co-evolved with
stinging nettle.
Maybe the chemicals were not designed to penetrate grazing mammals but
were designed
for scent so that a deer or buffalo smell the toxic chemicals and
avoid eating the plant.
Or, perhaps, the chemicals were designed to insects such as
grasshoppers that when
they traverse the plant some of those chemicals get on their bodies
and they irritate them.
I have never seen a grasshopper on the stems of any stinging nettle,
so I would bet it is
grasshoppers that are the main target of nettle.
Archimedes Plutonium
www.iw.net/~a_plutonium
whole entire Universe is just one big atom
where dots of the electron-dot-cloud are galaxies