With the hot weather of July have come the horseflies -- big, fast flying
747 brutes that can be heard crashing into the windows of our country home.
This afternoon I was sitting in the garage repairing our old lawnmower, and
had raised the smaller overhead door of the third bay in order to let in a
little breeze. Pretty soon here come the horseflies, zooming in through the
door opening. I noticed that they usually made a quick U-turn after
entering and zoomed out. Wishing to eliminate a few of them, I decided to
see whether I could get the door closed while one was still inside. This
proved not too difficult to do, but on one occasion I failed to get the door
completely shut and the fly managed to escape by homing in on the narrow
strip of sunlight that was visible at the bottom of the door. The fly moved
downward while keeping in contact with the door until it reached the opening
and then flew through. This was interesting because normally the flies
gravitate toward the ceiling and end up bouncing along it. On the remaining
occasions the door shut tightly and the trapped fly then quickly homed in on
one of the overhead lightbulbs illuminating the interior of the garage.
They'd circle it furiously and sometimes land on it, but evidently the bulb
surface was too hot for comfort as they always took off again less than half
a second after landing.
So at this point I'd say that horseflies have a positive phototaxis, i.e.,
they control for being in the light, at least when attempting to find their
way out of a blind alley if not always. They also seem to control for going
up as a tactic for finding their way out, although moving toward light takes
precedence. I don't know what variable they were controlling which brought
them into the garage in the first place: it could have been visual and/or
olfactory inputs associated with the presence of possible food (me; perhaps
I was serving as the bait for the trap), or perhaps entry into the garage
was purely a side-effect of having a big blind opening in the flies' flight
paths. The flies' quick attempts at exit after entering the dimly-lit
garage suggest that whatever control actions resulted in garage entry, the
results (dead end, reduced illumination) were unanticipated by the flies and
had to be corrected after the fact.
At any rate, a garage with an open overhead door that can be quickly shut
makes a great horsefly trap; I've gotten rid of 15 of the rascals thus far.
By smacking them hard with a flyswatter, I am able make them stop moving --
forever. I wonder whether Rick would say that I am coercing them to behave
that way. After all, I am controlling an aspect of their behavior, without
regard to the flies' wills . . . (;->
Where I used to live, in Gloucester, one can see enigmatic wooden boxes on
stilt legs out in the salt marshes. It was quite a while before I found out
what they are.
They are traps for greenheads. The greenhead is a vicious local cousin of
the horsefly. They congregate around the salt marshes. I expect maybe they
propagate there.
I don't know whether they are the same critter, but we've got a greenheaded
biting fly here, too. Unlike the horsefly, it bites almost instantaneously
upon landing on exposed flesh and takes a chunk out, leaving a bleeding
wound. Fortunately they haven't been numerous.
A greenhead trap is very simple. It might work for horseflies. It's a box,
painted a dark color, on four legs. The top of the box is covered with
window screen. The bottom of the box is closed except for a slot in the
middle. The slot is formed by two baffles that separate as they go up to
the sides at the top.
About how large are the boxes? How wide is the slot at the bottom?
The explanation given is that the flies approach them as warm-blooded
four-legged animals (they are warmed by the sun--that's one good reason for
the dark color). They fly under the belly of an animal to bite exposed
flesh where the fur is not so thick. When they fly under the trap, they see
light up through the opening. They fly from the shadow under the box toward
the light. When they get to the screen, they can't get out, and they don't
fly back down. Eventually they die.
Horseflies seem more likely to land on an animal's back, judging from what
I've seen of them pestering the local cattle, but it's worth a try. If it
doesn't get the horseflies, maybe it'll get those greenheaded vampires.
Less labor-intensive than the garage door and flyswatter.
But maybe not as _satisfying_?
You might want to
give it a try. Tell people you're a control theorist, and this is a model
of a horse (from a horsefly's point of view). This will ensure that they
don't expect you to build a robot for them any time soon.
Gotcha. They'll be surprised enough that I'm apparently doing research. (;->
Where I used to live, in Gloucester, one can see enigmatic wooden boxes on
stilt legs out in the salt marshes. It was quite a while before I found out
what they are.
They are traps for greenheads. The greenhead is a vicious local cousin of
the horsefly. They congregate around the salt marshes. I expect maybe they
propagate there.
A greenhead trap is very simple. It might work for horseflies. It's a box,
painted a dark color, on four legs. The top of the box is covered with
window screen. The bottom of the box is closed except for a slot in the
middle. The slot is formed by two baffles that separate as they go up to
the sides at the top. Here's the end view:
.......
>\ /|
>_\ /_|
>> >>
>> >>
>> >>
The explanation given is that the flies approach them as warm-blooded
four-legged animals (they are warmed by the sun--that's one good reason for
the dark color). They fly under the belly of an animal to bite exposed
flesh where the fur is not so thick. When they fly under the trap, they see
light up through the opening. They fly from the shadow under the box toward
the light. When they get to the screen, they can't get out, and they don't
fly back down. Eventually they die.
Less labor-intensive than the garage door and flyswatter. You might want to
give it a try. Tell people you're a control theorist, and this is a model
of a horse (from a horsefly's point of view). This will ensure that they
don't expect you to build a robot for them any time soon.
About how large are the boxes? How wide is the slot at the bottom?
I'd say about 1.5 ft. wide and tall and 2 ft. long, maybe a little bigger,
and the slot 2-3 inches wide. Bottom may have sloped upward toward the
slot, not sure. Could experiment with a cardboard box I guess before doing
something more permanent. Very likely it was developed by trial and error.
Horseflies seem more likely to land on an animal's back, judging from what
I've seen of them pestering the local cattle
That might be spurious explanation I was given, and it's just that
whichever flies do get under there go up toward the light.
The explanation given is that the flies go underneath looking for the soft
belly parts to bite and, not finding any, keep going up. Probably it's only
that those that happen to go under fly up toward the light.
I always wondered if they ever filled up, and, if so, what then. Never
looked inside.
The explanation given is that the flies go underneath looking for the soft
belly parts to bite and, not finding any, keep going up. Probably it's only
that those that happen to go under fly up toward the light.
Ah, come to think of it, that does make more sense. The large opening at
the bottom increases the area over which flies can enter, whereas the small
opening at the top minimizes the area over which the flies can leave; thus
discovery of the entrance is much more likely than discovery of the exit.
As seen from the bottom, the light eminating from the slit should tend to
attract the flies upward (positive phototaxis); meanwhile, those that alight
on the angled boards will tend to move upward against gravity (negative
geotaxis). Once through the slit, the flies will tend to congregate on the
screen. Now if it works on horseflies, that will be great . . .
By the way, I did a web search on horseflies, and most of the relevant sites
were Canadian. Guess it's a good thing the summers up there are short.