GLAD INSECTS DO NOT PREY ON HUMANS
October 18, 2009
wrote about a terrifying spectacle--an extinct eagle large enough to carry
off a person. Scary to be sure, but what if dragonflies got as large as
an eagle with a 12-foot wingspan? How awesome would that be?
has seen a dragonfly snare a horsefly for a meal knows what effective
predators they are, and like other insects, they are incredibly strong
for their size. Giant dragonflies would definitely mean fewer stray dogs
and cats in the neighborhood, and people would have to be careful going
from the car to the house.
are among the most effective of aerial predators. If they reached a weight
of 40 pounds, people would have some survival issues to worry about. Dragonflies
spend their first months in water as larvae called naiads. Naiads, which
look like something on the set of a horror film, are as dangerous to small
aquatic animals as the adults are to walking and flying creatures. Dragonfly
naiads, which can be more than an inch in length, have enormous jaws with
pincers on the front of the mouth. They eat a variety of small fish, tadpoles,
and larval salamanders.
we expect the naiad of a 40-pound adult dragonfly to look like: at least
30 pounds of nastiness that would be able to overcome the largest bass,
an adult beaver, maybe even a person swimming in a lake? Inland waters
filled with naiads would get as much media attention as a shark-infested
ocean beach. People would soon decide that swimming in lakes, rivers,
and reservoirs with naiads was no longer an enjoyable pastime. Water skiing
would become much more of an adventure and inevitably result in some sensational,
if gory, news stories.
as it is to consider a predator that could macerate us in the water and
then metamorphose into something that could cart us away through the air,
research on the impacts of true-size dragonfly naiads on tadpoles has
revealed results that are of special interest in themselves. Predators
use numerous tactics to capture their prey, which in turn develop defensive
traits to avoid capture.
in nature interacts with and is affected by other species, and every species
on earth today is a kaleidoscopic reflection of its evolutionary past.
A response to dragonfly naiads as predators on their prey was observed
by researchers at the University of Michigan in studies that led to a
better understanding of the adaptive response of prey to the presence
of predators. The ability of dragonfly naiads in a pond to alter morphological
development of prey was observed with frogs. The finding was documented
by raising tadpoles in waters with dragonfly larvae and without them.
When dragonfly predators were present, the shape of the tadpoles changed
of individual tadpoles were measured as an indicator of morphological
change. An image of a tadpole's tail fin, body, and tail muscle was placed
on a computer screen so that linear measurements could be made. The image
analysis approach allowed comparison of a large number of tadpoles from
predator-free situations with those from experimental ponds harboring
naiads. The rate of growth and development of tadpoles as they metamorphosed
into frogs was not affected, regardless of whether dragonfly predators
were present. For example, bullfrog tadpoles reached the same general
sizes regardless of whether naiads were there to eat them. However, tadpoles
reared with naiads showed significant morphological differences from those
raised without the presence of predators.
changes was that the would-be frogs developed deeper tail fins when predators
were present. Tadpoles use their tails for propelling themselves through
the water, so bigger tail fins would increase swimming speed. Being faster
when a voracious dragonfly predator is in the vicinity could be an effective
antipredator mechanism. It is remarkable that merely the presence of naiads
in the water would cause the tadpole's body to react in such a protective
appreciate the intricate species relationships and delicate networks that
comprise natural communities and make our world such a marvelous place.
We should also be thankful that dragonfly naiads do not reach the size
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