Date: Sun, 06 Feb 2000 14:05:58 +0000 From: Juerg Steiger <juerg.steiger@iae.unibe.ch> To: cp@opus.hpl.hp.com Message-Id: <aabcdefg368$foo@default> Subject: Re: Ping Observation/Question
Hi Ivan
>Many plants had housefly sized flying insects and a few even had
> great big dragon flies! Funny thing though, when I sprinkle
>live fruitflies on my butterworts here at home they nearly always get
>free from the plants and have no trouble doing so. So then, how can we
>explain the large size of the insects which are captured in nature?
I have observed the same phenomenon in other northern Pinguicula species:
Captured dragon-flies and crane-flies. My observations: In natural
Pinguicula sites there is usually high relative air humidity in the night,
the nocturnal temperature decline mostly resulting in dew. So particularly
in the early morning the Pinguicula leaves get extremely slimy. The
advantage of an increased amount of mucous juice seems to prevail the
disadvantage of its relative dilution. The more juice there is around the
more likely it is that the wings are sticked on and the wings are the
killer criterion. As a result even large prey cannot escape from the
trapping, each gland contact and each movement causes numerous mucous
filaments. As soon as their wings are In addition the leaves' margins begin
to fold in after a prey contact.
There are two kinds of larger insects trapped: Dragon-flies are day-active
and as most day-active insects they become stiff and sluggish in the low
night and morning temperatures. They are either captured during their
first morning flights or in late afternoon-evening. Those which cannot
liberate themselves before night will resign their efforts due to the
combination of weariness, general loss of activity in the darkness and
activity reduction due to the temperature decline. Dragon-flies captured at
noon-early afternoon can often escape.
Crane-flies are night-active and are attracted by wet substrate in which
their larvae feed. They are large but not as strong as the dragon flies and
they are hopelessly lost in the ample digestive juice caused by the
prey-stimulation plus the high air humidity.
These explanations are confirmed by the following observation: With my
greenhouse Pinguiculas I did not observe large prey as long as I kept the
plants in medium air humidity, although insects had access to the plants.
But three years ago I installed several ultrasonic humidifiers, resulting
in relative air humidity of 97-100 percent each morning. Since then I also
observe occasionally large crane-flies and smaller dragon-flies captured by
the Pinguiculas (including P. macroceras ssp. nortensis) which erroneously
get into the greenhouse. At noon time air humidity decreases to about 60
percent, the secretion droplets of the mucous glands get smaller and the
leaves look dryer. Of course at the higher noon temperatures day-active
insects are more alert and 'stronger'. This allows even smaller insects
(particularly 'Schwebefliegen' - I just forgot the english term) to escape
before their wings are sticked on.
Kind regards Juerg
This archive was generated by hypermail 2b30 : Tue Jan 02 2001 - 17:35:05 PST