Miller Moth Behavior in Southern New Mexico
Sloan Digital Sky Survey Telescope Technical Note
19970220
Matthew Buffaloe
University of Washington
Contents
Introduction
During the summer months, a regular plague of moths occurs in the
mountains of the southwest deserts of the United States. Apache Point
Observatory is located 2800 m (9200 feet) above sea level in the
Sacramento Mountains of south-central New Mexico. The intensity of
the plague varies from year to year; near the peak of a bad year,
hundreds of moths are captured per day inside the observatory
buildings.
The moths have a variety of behaviors. Most troublesome to us is
that they seek dark tight spaces. The telescope axes at the
observatory are moved by friction between a motor-driven capstan and
a large drive disk, to which the telescope is connected. The
capstan-disk interface is apparently attractive to moths. When the
telescope moves, moths are often crushed at the interface. The
resultant contamination may cause encoder errors, causing the
telescope to point and track poorly until the surfaces are thoroughly
cleaned. The result is lost data and telescope time. In other
locations, moths interfere with the operation of shutters and other
mechanisms.
The goal of the study reported herein was to study moth behavior
in an attempt to develop means of reducing their impact on
observatory operations. A moth abatement system must be compatible
with several constraints.
- The areas most affected are enclosed and frequented by
observatory personnel as well as moths. This makes the pesticide
use unattractive unless it can be kept localized.
- It must not interfere with the operation of the telescopes.
Solutions involving lights, heat sources, vibration, and sound may
not be satisfactory.
- The flow of air through and around the telescopes and
telescope enclosures is managed carefully to minimize image
degradation. Modifying these flows so that a chemical attractant
is dispersed properly may not be possible.
Figure 1: Images of moths. The images on the
right show crack-seeking behavior. The upper right image shows a
number of moths that have sought the space behind the blinds between
the window handle and frame.
Trapping Moths
Trapping moths allows regular sampling of the population for
species identification. Also, the comparison of various trap designs
gives insight into moth behavior.
A series of cardboard boxes were constructed with varied orifices.
These boxes were simply placed around the lower portion of the 2.5m
telescope enclosure at varying heights. Box #1 had a 0.2 inch slit,
oriented along the length of the box. Box #2 had a circular hole with
a diameter of 0.3 inch. Box #3 had a corner cut off. Box #4 had 0.3
inch slit in the side with interior walls running the length of box
closing off the open space. Box #5 was similar to #4 except that the
slit was on the top of the box. Box #6 was similar to #1 except that
the slit was oriented with the width of the box. Box #7 had a 0.3
inch square hole in the top with the inside left open.
The traps were placed in the lower level of the Sloan Digital Sky
Survey (SDSS) 2.5-m telescope enclosure unless noted otherwise. The
enclosure is braced by pairs of angle iron placed so that there is a
10 mm gap between the angle iron. These gaps contained tens of moths
most of the summer of 1996, a light moth year.
The boxes were placed on the floor. The next morning, they were
checked for moths. One moth was found in each of boxes #1 and #4. The
boxes were checked again three days later. There were no moths in any
of the boxes. After another three days the boxes were checked and
moths were found under the boxes. The boxes were then turned to
conceal the openings. The next morning no moths were found in or
around them.
Due to the lack of success with the boxes simply set around the
room, selected boxes were affixed directly to the angle iron
inhabited by the moths. Box #1 was suspended under the angle irons
with the slit of the box matching that between the angle iron. Boxes
#4 and #5 were set similar to #1 except they were placed on top of
the angle iron. Box #6 was set on top of the angle iron with its slit
oriented vertically just to the side of the gap in the angle irons.
Six days later, these traps were removed and put into plastic bags.
They were then placed in the kitchen freezer to kill the moths
without damaging them. When the box traps were removed from the
freezer boxes #1 and #6 had no moths in them. Box #4 had one moth in
it, while box #5 had nine moths.
A week later another attempt was made to trap these insects. Boxes
#1 and #6 were cut to allow a night light to be inserted into each of
the boxes. Box #1 was lined with foil tape to create a shiny
reflective surface, while box #6 was lined with black cloth tape to
give a dull, dark surface. These boxes were set, with lights on, in
the operations building, in a dark room. They were checked the next
two mornings with no success.
Having found that the design of a space consistently attractive to
moths was much more difficult than assumed, a moth sample was
obtained by searching for them in existing hiding places and catching
them by hand.
Once a suitable method had been established an entomologist at the
New Mexico State Department of Agriculture was contacted. A series of
samples were taken to be identified. The sample of moths collected in
early July in the 2.5m telescope support building were identified as
Order Lepidoptera, Family Noctuidae, Agrotis ypsilon. Samples
collected in late July and early August, from the lower portion of
the 2.5m telescope, contained the same species. The larvae of this
moth eats a variety of broad-leaf plants and grasses. They have a
life cycle of approximately 30 days. This species winter in the
southern U.S. and Mexico. As spring temperatures rise the moths
migrate north. It is possible that these moths live in the area
around Observatory all year.
A sample had been collected between the summers of 1995 and 1996.
They were collected from the backs of various drawers and window
sills. The collection contained 9 of the Agrotis Ypsilon. There were
also 4 Bulia deducta, of the Family Noctuidae.
Three larger species were also captured at the observatory. The
first was Hyles lineata of the Family Sphingidae. The second was
Coloradia pandora Blake of the Family Saturniidae. The third remains
unidentified, but is believed to be of the Family Saturniidae, as
well. None of these three species were noted more than twice around
the observatory.
Vibrations and Sounds
It has been noted that during storms moth activity increases. This
is especially true during hail storms. It is also believed that moths
are sensitive to ultrasonic, due to the fact that they are reportedly
a food source of bats. The jangling of keys has produced a sound that
caused moths to become agitated. Due to the sensitive optics involved
with the telescopes on site, if the vibrations were to be
investigated they had to be dealt with very carefully.
One experiment along this line of inquiry was to strike various
portions of the building and look for a response from the moths. This
was carried out in the lower portion of the 2.5m telescope enclosure.
A mallet with a rubber tip was used to prevent any damage to the
building. With the mallet the building was struck systematically,
beginning with the walls. The moths showed no sign of annoyance. The
process then moved to the wall beams. Again the moths were unaffected
by the hammering. This carried on to the floor and the beams
containing the moths, themselves. The moths seemed to be uninterested
until the hammering was within a few inches of directly outside their
position between the support beams.
On the same afternoon as the hammering experiment, a similar test
was performed. Various loud stomping and clapping noises were made.
This was done throughout the room. As above, the moths remained
unaffected until disturbance was made quite near to them. Anything
further than foot away did nothing.
Based upon the fact that moths are preyed upon by bats the
observatory acquired a number of ultrasonic bug repellents
approximately a year ago. These devices, once plugged into an
electrical outlet, are supposed to emit an ultrasonic sound that is
disturbing to moths. Unfortunately, these devices have yet to have
any noticeable affect on the moth population around the observatory.
A signal generator and a small self-amplified speaker were set-up
in the lower portion of the 2.5m telescope enclosure. The speaker was
aimed up, in the general direction of a large cluster of moths
between the beams. The amplitude was set at 2 Vpp so as not to damage
the speakers. The volume was changed by controls on the speaker
itself. The frequency of the signal was varied from 200 Hz to 200
kHz. The sounds produced no affect on the moths, except in the range
of 10 kHz. At this frequency the target cluster became excited for a
moment, but very quickly settled back down. After 19 kHz no audible
signal could be detected from the speakers. The speaker's
effectiveness was questioned but not investigated. This data is shown
in Table 1.
Table 1: Moth frequency responses. A range of sounds were
created using a signal generator attached to a speaker. Moth
response to each sound was noted.
Amplitude Frequency Reaction
2 Vpp 0.2 kHz none
0.3 kHz very slight
0.4 kHz startled but settled soon
0.5 kHz none
0.6 kHz 1 moth noted moving briefly
0.7 kHz none
0.8 kHz none
0.9 kHz none
1.0 kHz none
1.1 kHz none
1.3 kHz none
1.5 kHz none
3.0 kHz none
5.0 kHz none
10.0 kHz disturbed but not moving
11.0 kHz disturbed but not moving
12.0 kHz disturbed but not moving
14.0 kHz disturbed but not moving
16.0 kHz none
18.0 kHz none
20.0 kHz none
40.0 kHz none
60.0 kHz none
80.0 kHz none
100.0 kHz none
200.0 kHz none
Due to the interesting response noticed at a frequency of
approximately 10 kHz, the equipment was used to create a chirping
sound. With the signal generator a frequency modulation mode was
used. The amplitude was set as previous, while the frequency was set
at 10 kHz. The span was set at either 1 kHz or 2 kHz. The rate was
set at 5, 10, 15, 20, or 100 Hz. Beyond momentary agitation, the
moth's showed no concern toward the signals. This test was also run
at 15 kHz with spans of 1 and 3 kHz and a rate of 100 Hz. This again
did nothing to the moths.
Air Jets
A number of casual observations have been made by the staff of
Apache Point Observatory. One of the more interesting items involves
the blowing of air over moths. It has mentioned a number of times
that this has a profoundly disturbing affect.
This observation led to a conceptual deterrent system. This system
involved a system of air hoses running to all of the drive
assemblies. These hoses would release jets of compressed air at
prescribed intervals.
For this system some hardware was acquired earlier this summer. An
electric timer and a small three way air valve had been ordered.
Unused small rubber tubing with an inside diameter of 1/8 inch was
located on site for the plumbing. An air gun and array of nozzles
were ordered to facilitate testing of a prototype. Upon inspection of
the timer it was noted that it would not give differing on and off
times. To solve this problem another identical timer was purchased to
put in series with the first. When inspecting the drives of the
various telescopes it was noted that no matter which telescope this
system was to be implemented on, sharp corners were to be navigated.
To accommodate this, 3/16 inch outside diameter, thin wall stainless
steel tubing was acquired.
Throughout the summer a variety of tests were run to answer
questions mainly regarding effectiveness and efficiency. One of the
more interesting tests began as an inquiry into the movement habits
of the moths in the lower portion of the 2.5 m enclosure. To begin,
the room was divided into sections. Moth populations were counted for
each section. At this point there were 108 moths found in the room.
With the use of the air gun all of the known moths were forced out of
the beam gaps they were inhabiting. After this disruption a periodic
population count was made over the next 11 days. The population on
the eleventh day was 29. This accounts for just over 1/4 of the
original, known, population. A thorough search of the room was
conducted with no more moths to be found. Another note of interest is
that while the disruption was occurring, one of the staff was in the
upper portion of the 2.5 m enclosure. No surge of moths coming from
below was noticed.
To further look into the effectiveness of the system, a test was
devised to gain some knowledge regarding the strength of a moth. The
main test apparatus consists of a clear piece of PVC pipe with a 1
7/8 inch outside diameter. At one end of the tube is attached a
funnel. Through this funnel is inserted an air nozzle. For the
experiment the steel tubing was used due to its use in the planned
system to be implemented. At the far end of the tube is a perforated
cap. This is to allow reasonably free air flow while preventing the
moth from escaping. This setup is shown in Figure 2. While monitoring
the moths distance from the nozzle, air jets were directed at them.
The pressure of the compressed air was varied to give different air
speeds.
A couple of interesting observations were made. First, these
creatures are very strong. They were able to handle upwards of 80 psi
so long as they were more than five- six inches from the nozzle. Once
they moved within the prescribed distance they were dislodged by 50
psi. It should be noted that these moths showed signs of annoyance
with as little as 20-30 psi. The second observation of interest had
to do with the moths reaction when experiencing a jet. The moths had
a tendency to "hunker down" and wait until the jet had stopped.
Figure 2: Air jet test setup. Testing
apparatus used to gain information regarding strength of moths. The
same equipment was used to relate pressure of the compressed air and
the velocity of the jet experienced by the moths.
With the same setup as above a test was performed to relate the
pressure of the compressed air and the velocity experienced by the
moths. A series of holes were drilled into the PVC tube to permit the
insertion of a pitot tube and an anemometer. These holes were drilled
at six inch intervals starting at 12 inches and going to 30 inches.
When a hole was not in use it was taped over to maintain continuity.
This information concerning velocity was then used to estimate flow
rate. This information is given in Table 2.
The anemometer measurements are sensitive to air pressure
differences. Due to the high altitude of the observatory, the reading
from the anemometer had to be corrected. The values in Table 2
reflect this correction.
Table 2 : Flow velocity and volume. For each gauge pressure the flow
velocity was measured at each of the four ports drilled into the pipe.
An average of the four velocities was calculated. From the average
flow velocity, flow volume was calculated in both english and metric
units.
Pressure Tube Pitot Corrected Average Flow Flow
port velocity anemometer velocity rate rate
psi ft/min ft/min ft/min ft^3/min m^3/min
20 1 291.2 251.3 254.8 3.39 0.0959
2 230.2 241.3
3 243.6 243.8
4 291.2 245
30 1 318.9 375 337.9 4.49 0.127
2 318.9 352.5
3 318.9 360
4 308.8 350
40 1 371.2 475 406.3 5.4 0.153
2 356.6 450
3 356.6 446.3
4 356.6 437.5
50 1 493.7 581.3 515.8 6.86 0.194
2 493.7 555
3 482.8 550
4 424.4 545
60 1 524.9 622.5 581.8 7.74 0.219
2 544.7 620
3 554.3 615
4 563.8 608.8
70 1 642.9 697.5 660 8.78 0.249
2 651.1 690
3 642.9 683.8
4 591.3 680
80 1 675 750 727.7 9.68 0.274
2 727.9 743.8
3 727.9 736.3
4 720.6 740
Once all of the hardware had been assembled a prototype system was
constructed. The system is controlled by the two previously mentioned
timers set in series. The first timer was set to cycle on and off at
seven seconds. The second timer gives a burst of one second at the
beginning of every on cycle. This gives a total off time of 13
seconds with an on time of one second. The solenoid was plugged into
the second timer. The air was supplied by the main site compressor.
The regulator on the air outlet was set to 45 psi. This outlet was
then connected to a reservoir tank to prevent excess back pressure
effects. The solenoid was then connected to the reservoir tank. A
single rubber tube was connected to the solenoid. This tube was then
divided into three tubes. The assembled hardware for the prototype is
shown in Figure 3. This contraption was set on the altitude drive of
the 3.5 m telescope. The three rubber tubes were pointed into
separate portions of the drive. Figure 4 shows the upper two tubes
pointing into the drive assembly. Figure 5 shows the third last tube
pointing up into the drive from below. This prototype ran for about
two weeks with no ill effects noted. In addition there was no report
of moths being run over by the altitude drive. This was not
conclusive because only a small number of moths had been run over all
summer. A week after removing the prototype system the wheel was
checked and at least two carcasses had been squashed. These insects
were squashed after the removal of the air jets.
Figure 3: Prototype hardware. This is all of
the hardware used in the prototype air jet system. This shows the
system just after being assembled, and just before installation.
Figure 4: Upper jets of prototype system.
This photo shows two of the nozzles of the system. They are directed
into two separate contact points on the upper portion of the altitude
drive of the 3.5m telescope.
Figure 5: Lower jet of prototype system. This
photo shows one of the nozzles of the system. It is directed up into
the lower portion of the altitude drive of the 3.5m telescope.
In an attempt to more clearly prove the effectiveness of this
system one more test was performed. The main idea behind the test was
to attract moths to a specific surface. This surface was divided into
two portions. One side would have a jet of air periodically blown
across it. The first model of this test consisted of a foil lined box
with a small light in it. This had a piece of plexi-glass for the
surface. The light was to be the attractant. This was left overnight,
in the base of the 3.5 m enclosure, and recorded on a video cassette.
Due to poor lighting the video recording was completely
unintelligible. This test was attempted again the next night using a
video monitor, producing a white light. The recording of that night
was much clearer. However, no moths were seen on the screen. In an
attempt to test a larger population the test was moved to the lower
portion of the 2.5 m enclosure. Again no moths visited the screen.
The question was raised as to whether the air jet scared the moths
away before they could be detected on the screen. For one night the
air jet was disconnected. The screen was also adjusted to give a
slight flashing appearance, in an attempt to be more appealing to the
moths. Inspection if the recording showed, once again, no moths
present.
Lights and Zappers
While doing initial surveys of moths populations in the 2.5m
enclosure it was noted that the moths were disturbed by the
flashlight beam. When the light was pointed at them, they would
quickly move out of the beam.
To further investigate this activity a desk lamp was affixed to
one of the beams in the lower portion of the enclosure. The light was
directed down upon a cluster of approximately 10 moths. Six of the
ten moths moved away as soon as the light was turned on. By moving
away, all the moths did was remove themselves from the direct beam of
light. They were still in a well lit area. Within an hour, one more
of the insects had moved. The next morning there were still three
moths in the light, but they had moved out of the direct beam. By the
third day only one moth remained and it was well toward the fringe of
the light. On the fourth day two moths were present, but they were
essentially out of the light. Since an incandescent lamp had been
used for the experiment, heat was suggested as the driving force
behind the moth exodus.
This question led to the use of a fluorescent lamp in the same
experiment. The light was set over a cluster of 15-20 moths. Within
10 minutes of the light being turned on all of the insects had moved
out of the beam. The lamp was then turned off. Two days later the
light was moved over a new cluster of approximately 30 moths. As soon
as the light was turned on the moths began moving. Within three
minutes at least half of the cluster had moved off. By five minutes
only approximately a third of the original population remained. After
10 minutes, six moths remained. After 1.5 hours all the moths had
moved out of the light. A large cluster had formed toward the edge of
the light. The light was then turned off. Two days later the light
was turned on over a cluster moths. The experiment was neglected
until the next morning. The cluster of moths had not moved out of the
light.
Earlier in the year the observatory purchased a common insect
zapper. The zapper consists of two black lights with a grid of wires
hanging from between the lights. When a moth strikes the grid an arc
is formed and the insect is electrocuted. Due to the dependency of
the dielectric constant of air on pressure and the high altitude of
the observatory, the grid would arc violently simply by plugging it
in to the wall outlet. The manufacturer sent two capacitors to be
hooked up to the grid, in order to try and reduce the voltage. These
did not have enough of an effect. Instead a variable line voltage
transformer was connected to reduce the voltage. This worked fine for
the grid, however, the lights required full voltage. The zapper was
rewired to accommodate this. The zapper was then installed in the
intermediate level of the 3.5m telescope. A wire basket was hung from
the zapper to collect the moths. This was necessary because of the
fact that the zapper was hung on a beam that rotates with the
telescope while the floor remains stationary. Without the basket moth
carcasses could have been spread all over the floor of the level.
After a week of running the zapper, it was suggested that the
insects are attracted to the infrared as opposed to visible or
ultraviolet light. To test for this an incandescent bulb was affixed
to the zapper above where one of the black lights would have been.
The black and incandescent lights were alternated from night to
night. There were also two periods for which no light was turned on.
This was done to see how many moths would randomly run into the
zapper. A table and graph of the carcass counts from night to night
are shown in Table 3 and Figure 6.
Table 3: 3.5-m Telescope Moth Zapper. A bug zapper was
set up in the intermediate level of the 3.5m telescope.
The number of moths killed each day was recorded.
Different lights were attached to the zapper to try and
determine moth attraction. On two occasions no lights were
turned on, to see how many moths would randomly run into
the zapper.
Date(Aug.) Light Moths Killed Moths/Day
1 Black 11
2 Black 19
5 Black 144 48
6 Black 14
7 Incandescent 9
8 Black *197
9 Incandescent 12
12 Black 73 24
13 Incandescent 25
14 Black 10
15 Incandescent *54
16 Black 25
19 Incandescent 48 16
20 None 1
21 Black 31
22 Incandescent 14
27 None 9 1
28 Incandescent 18
29 Black 12
Figure 6: 3.5-m telescope moth zapper. This
is a graphical representation of Table 2.
The asterisks refer to days with heavy storms, which may account
for the increased activity. The gaps in the data occurred during the
weekends when the zappers were left unattended. The large counts
after each weekend reflect multiple day accumulations of moth
carcasses.
When the capacitors did not work to solve the arcing problem, the
manufacturer sent a replacement model of a lower voltage. Upon
receiving the new zapper it was tested and found that it arced as the
first did. It was, however correctable with a single capacitor. This
second zapper was hung in the Monitor Telescope enclosure. This was
facilitated by the fact that the telescope had been taken apart for
maintenance. With this zapper, the feasibility of running the zapper
during the day and turning it off at night was tested. The moth
carcasses were counted twice a day: once in the morning and again in
the evening. This data is shown in Table 4 and Figure 7.
Table 4: Monitor telescope moth zapper. A bug zapper was
set up in the observing level of the Monitor telescope. The
number of moths killed by the zapper was counted at the end
of each night and day. This was to determine the
effectiveness of using a zapper to control moth population
during the day, while the telescope would be inactive.
Date(Aug.) Day/Night Moths Killed Moths/12hr
12 night 12
13 day 5
n 9
14 d 7
n 9
15 d *25
n 9
16 d
weekend 28 4
19 d 3
n 4
20 d 10
n 1
21 d 5
n 2
22 d 2
weekend 28 3
27 d 1
n 1
28 d 3
n 1
29 d 0
Figure 7: Monitor telescope moth zapper. A
graphical representation of Table 4.
In an attempt to add to our information regarding light related
behavior a letter was posted on an internet newsgroup;
sci.bio.entemology.misc. The response suggested a scientific company
that sells insect light traps. This company was contact and a portion
of their catalog was acquired. Upon inspection these traps were
largely cleaner versions of a bug zapper.
Natural Predation
Sometime in mid-July a dead bat was found in the lower portion of
the 2.5m telescope enclosure. This implied the presence of bats in
the area and suggested the possibility of natural predation as means
of controlling the local moth population. The entomologist at the New
Mexico Department of Agriculture was contacted. The question was also
referred to the NMSU's Extension Wildlife Agent. It seems that while
some bats do eat moths, not all species do. It was not clear whether
those in the vicinity of the observatory preyed upon moths or not.
The bat population can often be locally increased by providing
artificial bat houses. Bats are rather selective about their houses.
They prefer high, stable temperatures in their roosts. Unfortunately,
bats often find suitable habitats in or around human dwellings. Cases
have been reported in which there were so many bats in the attic of a
house that the owners could no longer insure the building.
Coincidentally little, or no, decrease in the local insect population
was noticed.
Conclusions
- The construction of spaces consistently attractive to moths is
more difficult than previously assumed. It may be that moths avoid
certain shapes, surface finishes and orientations. If so, it may
be possible in the design of instruments to include features that
moths find unattractive. More research is needed.
- Trapping of moths is efficiently done by hand.
- Vibration and sound experiments produced inconclusive results.
Few man-made sounds or vibrations caused significant disturbances
of moths. However, they are affected by rain and hail storms.
- The data regarding moth response to light is inconsistent.
Common lore is that moths are attracted to light. Indeed, the
lighted bug zapper is effective. This study also noted that a
variety of lights repelled moths under different circumstances.
- There are two ideas regarding the effectiveness of the bug
zappers. The first being that during a storm the zapper kills a
reasonable portion of the population. This means that during
normal conditions only a small fraction is killed. The other idea
suggests that there are two separate populations. The mobile
population, of which a reasonable fraction each day are killed,
and a stationary population, which poses no threat to the
telescopes. By the first the zapper is doing little good.
According to the second the zappers are effectively reducing the
nuisance moth population.
- Air jets appear to offer the most effective solution. The data
is not entirely conclusive. It is fairly clear that moths find air
jets quite uncomfortable. The fact that two moths were run over
after the prototype was removed, and none during its use, does
imply some degree of success.
- While the idea of natural predation is an attractive one, it
has not been demonstrated that bats eat moths or decrease the
population density significantly. Also, the problems of providing
suitable houses and avoiding bat infestation of observatory
buildings must be solved.