Prey capture by Dionaea muscipula A review of scientific literature with supplementary original research.
Stephen E. Williams and Siegfried R. H. Hartmeyer (2017). Carnivorous Plant Newsletter Vol. 46/2: 44-61.
Keywords: Dionaea muscipula,
Venus flytrap, habitat, prey attraction syndrome, alluring glands,
nectar secretion, red color, scent, UV-reflection, fluorescence, size
selection, capture rate.
Many descriptions of prey capture by Dionaea muscipula (Venus flytrap)
in popular publications and educational literature are inaccurate. Here
we review well documented literature on prey capture in this
plant’s natural habitat and add observations on prey capture and
attraction mechanisms we have observed in plants cultivated in a
greenhouse and garden. Despite its common name “Venus
flytrap” does not specialize in capturing flies. About 70% of
the prey it captures in its native habitat consists of spiders, ants,
and beetles. Flies are only oneto-eighteen percent of what it captures.
In a greenhouse where flies, capable of entering the vents, composed
most of the available prey, over 90% of the prey captured were flies.
Dionaea cultivated in a garden captured a diverse array of animals,
only about 37% of which were flies. Dionaea is a generalist, capturing
a wide variety of prey species. Its capture mechanism does not appear
to have a “syndrome” analogous to the Pollination Syndrome
in flowers where a specific floral type is pollinated by a specific
animal (i.e. Bee Flowers or Fly Flowers). The measured capture rates of
Dionaea are low, about one capture/leaf/month in its native habitat.
Similar but lower rates were measured in the greenhouse and garden. The
single measurements in each habitat need to be repeated, but the low
rates are consistent with the observation that wherever it is observed
Dionaea has nearly all of its traps open. Both the low capture rates
and the large number of open traps suggests that alluring agents
drawing prey either do not exist or are ineffective. Despite reports of
nectar secretion by Dionaea traps, our observations show that
unstimulated traps are always dry unless wet by rain, condensation, or
a sprinkler system. Secretion occurs only after prey capture. Alluring
glands along the outer trap margin have been reported to be visited by
small ants that work their mouthparts over the glands. We have
photographed a fly exhibiting the same behavior. The exact nature of
this behavior needs to be further investigated, but it does not appear
that this attractant can act at a distance since flies are as likely to
land on the outside of a trap as on the inside. Darwin proposed that
the trap closure mechanism allows small prey to escape, preventing the
expenditure of energy on captures likely to be of little benefit.
Recent measurements of prey captures indicate that traps show little
selectivity based on prey size and that while traps could, in theory,
select larger prey, statistically they do not behave this way.
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