“The Burning Question,” asking if environmental damage

Texas Parks & Wildlife August 1994 pp. 38-43
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by H eather Millar
cross T exas, you hear the fire
ant stories:. farmers tell of
newborn calves blillded and
sometimes killed. Wildlife
managers say the insects
swarm over deer fawns who
try to lick them off, only to be stung
even inside the stomach , wh ere autop­
sies have found fire ants in the hlll­
dreds. Birders have discovered fire
ants climbing into nests to eat blne­
bird hatchlings. Small anim al
researchers say they lUust treat their
live traps with insecticide or find their
subj ects stripped to the bone by the
voracious hordes.
Are the fire ants exterminating
other forms of wildlife? Listening ro
the anecdotes, it's easy to get the idea
that fire an ts are all insect juggernaut
killing everything young, slow or
defenseless in their path. Anyone
who's suffered a fire ant's burning
sting, a.nd lived with the blisters for as
long as a week afterward, wonld find
little reason to doubt that fire ants are
a sco urge upon the land. \.\That's been
missing, however, is hard scientificevi­
denee to back up the hunch that some­
thing major is going on.
"Fire ants are causing a major revo ­
lution in the structure of natural com­
munities. It's puzzling th<lt ie's been
proceeding unnoticed under Oill very
noses," said Dr. Sanford D. Porter, a
fire ant speciahst for the United States
Department of Agriculture. "We still
don'tknownearlyenough aboutwhaes
happening here."
Slowly, however , evidence is monnt­
ing tha t fire ants do affect wildlife. In
15 Texas counties, a study funded part­
ly by the Texas Parks and Wildlife
D epartment found that after the inva­
sion offire ants, the population of bob­
white quail dropped by50 percent. "We
were floored by these results," said Scott
Lutz, a study participant and an assis­
tant professor of wildlife management
atTexasTech U niversity. "Other states
haven't seen the dramatic reduction in
wiidlife that we have seen in Texas. We
wonder if it's because we have more
multiple-queen mounds here."
Scientists aren't sure if the insidious
"multiple queen " or "polygyne" fire ant
Fi1'e ant mlJtmds, l"igbt, appear rapid­
ly in spring and f all a/te-r rainy periods.
Th e imported fire ant, (lbove, if believed
to have arrived in tbe Us. on produce
ships from South Ame1";ca. Bio/fJgists
believe thatfire antsare driving out othe-r
species, but they :ion't yet have the dilta
to p7"O'Ve it.
is a different species or subspecies of
the "single queen »ant. Buttheydo know
that mul tiple-queen mounds are more
destructive and harder to kill. This form
is central to the efforts of several
researchers who now are attempting
broad, ambitious studies ofhow fire ants
affect the ecosystem.
Texas Parks & Wildlife August 1994 pp. 38-43
The discovery of multiple queen colonies makes us wonder: could
the fire ant invasion be even worse than we thought?
Most o f Texas also has, or had, tvlO
types of native fire ants-native in the
sense that they arrived from Latin
America 500 yea rs ago. They too are
stinging ants, but their be havior is less
aggressive and their bite milder than
that of their recently arrived cousins,
Solenopsisinvicta, the aptly named "invin­
cible ant."
Invicta is a dark reddish-brown crea­
native to western Brazil and parts
of Paraguay and Argentina. It first was
found near southern port cities afoWld
1918. For this reason, it's commonly
believed that this ant, also called the
"imported fire am," smnggled itselfinto
thiscoun ttyaboard produce ships frOill
South America. No one knows for sure.
But everyone recognizes thatlnvitta has
thrived on foreign soil. It has no known
tuIe
natural enemies in North America and
its mounds have advan ced steadily until
they now cover 1I states, inclnding 60
million acres in Texas:
The immigrant ant's weapon of
choice is a fi ercely burning venom, an
o ily alkaloid mixed with a littl e protein.
Once aroused to attack, the insect
steadies itself by gripping the victim 's
skin with jaw- like pincers call e d
Texas Parks & Wildlife August 1994 pp. 38-43
mandibles. Then it injects venom into
the,;crim with its stinger. Unlike bees,
wruch.eviscerate themselves when they
sting, fire ants can sting again and again
,vithoutharmingthemselves. Theyalso
can dragtheir"sting"alongthe ground,
leaving a chemical trail to guide other
ants to the hapless victim.
ire ant attacks usually paralyze
other insects. The ants the u cau
consume them at their leisure.
Larger animals usually feel a
prickling sensation, followed by
intense bumingand blistering of
the skin. E nough bites can lead to a toxic
reaction iu small children and animals.
For those allergic to it, the venom's pro­
tein can canse flu-like aches and fever,
even anaphylactic shock and death.
For many decades, entomologists
beheved that colonies of these fiery
insects had only a singl e queen. Like
bees, the worker fire ants executed any
pretenders to the throne. Accordingly,
pesticides, marketed under va rious
names, targeted the queens. They
sought either to stop reproduction or
to get the foraging ants to share taint­
ed bait with the restofthe mound, espe­
ciallythe egg· laying queen. After a delay
of a day or two, the toxin would kick
into action, eviscerating all the ants that
had eaten it. With any luck, the queen
would be disemboweled too; and the
mound would die.
Then in 1973, a USDA researcher
was digging up some fire ant nests near
Hurley, Mississippi, and came across a
phenomeuon never before reponed .
Instead of One queen, the researcher
found "20 or 30 big fat girls that looked
like queens." Even moresnrprising, the
worker ants weren 't e.xecuting the com­
petingqueens.Instead, the worker ants
surrouuded all the queens to protect
them. The USDA dubbed the find
"queen city."
At first the reaction in the academ­
ic world was disbelief. Yet reports of
multiple queen colonies soon began to
come in from Georgia and Florida, and
then from Louis iana and Texas.
Researchers called thenew form "poly­
40 August J994
gyne." These renegade fireant colonies
seemed to be a new and improved
form, with queens Tn the dozens, even
hundreds. Fire ant populations swelled
with the output of so many more egg­
layiug monarchs. Multiple -queen
mounds could mean 10 rimes more fi re
ants, enough to over~vhelm most other
species in an area. Perhaps thinkingwish­
fully, most researchers theorized that
multiple-queeu mowlds made IIp only
a small fractioo of the total uumber of
fire ant mounds.
In 1991 , they found out they were
wrong. Taking a census of fIre ants in
Texas, researchers found the ants had
taken hold in most of the eastern part
ofthe state. Even more surprising, they
discovered that the majorityofmounds
housed multiple queens, and that there
were twice as many mounds in themul ~
tiple-queen areas. Once they had
thought that fire ants could at least be
controlled. Now that didn't seem so
clear. The researchers concluded that
the fire ant problem in Texas is much
worse than previously thought.
Asked if fire an ts are wi ping out other
creatures,MarkTrostieused a field near
Austin as au example. The Texas
-
Department of Agriculture researcher
said tllat J0 years ago tI,ere were only
twO or three fire ant mounds in that
field. There were more than 30species
ofother ants. Then the multiple queen
fire ants moved in, he says, exaspera­
tiOll evident in his vo ice. Now there are
so many fire antmounds, a person could
cross the field just by jumping from
mOlUld to mowld .
"It's unsightly, all those mounds.
The multi-queen fire ants are impact­
iug immensely," Trostle said. "I have
uo doubt that they're driving out lizards,
mice, snakes and whatever else gets in
their way."
Researchers have begun askingsome
disturbing questions: ·What if the auts
with many queens were a new species
or a hybrid, the result of SOffie envi­
ronmental disturbance' Whatifthe pes­
ticides people were using killed more
single-queen colonies thau those with
multiple queens? Might we be creat­
ing more territory for a more deadly
ant? TexasA&MProfessor S. Bradleigh
Vinson and many others started tryiug
to find out.
Les Greenberg, oue of Viusou's
graduate students, has spent almost a
Texas Parks & Wildlife August 1994 pp. 38-43
Biologists are finding 71)hite-tailed deer fawns
that have bem mmg 1'epeatedly bypre ants, left.
The ants tlppm'ently are attracted to the j{17JJn
by th e 'moisture t1rfllmd the eyes and nose.
Dm'£ng a food, colonies offire ants can foatlar
days, above, until they reach a spot where they
con reestllblish the;r colony.
decade creating multi-queen colonies
in his College Statiou laboratory. To
an unprac ticed eye, the ants that conld
be the grim reaper for mnch of Texas
wildlife look surprisingly unprepos­
sessing. T hey live in a laboratory room,
a small, wi nd owless rectangle mth
industrial-looking staiuless steel shelves.
D ozens of plastic boxes line the shelves
and each box essentially is a "mound."
W ithi n, the nlsty-colored insects teem
in th e millio ns. T hey look like delicate,
living foa m mo ving over the clods of
dirt they call ho me.
Vinson 's lab is comparing the DNA
of single-qneen and multi-queen ants.
T hey h ave found some differences, bnt
have yet to ga ther conclusive ev:idence
to prove whe th er the multi-queen ants
ar e a diffe rent species, or simply a
socially progr essive variant. Similar
work is going on elsewhere. A University
ofG eor gia lab has found that the multi-
queens lack an enzyme that single
queens have. While the exact classifi­
cation of multi-queens remains np in
th e air, resea rch ers have found that
multi-queeu ants behave differendy, in
ways that make them mo re snccessful,
hard er to kill and mo re of a threat to
other wildlife.
n ts that livein acolonywith alle­
giance to onl y o ne queen are
fi ercely te rritorial. They build
broad, conical mounds about a
foot high and will attack any­
thin g that com es too close,
including fir e ants fro m other mounds.
These in ter-mound conflicts keep down
the to tal fi re ant population in a given
are a.
Multi-queen fire ants, by co ntrast,
do n't fight. T hey slowly absorb other
m ounds, uniting them in a sort of
"super colo ny." Free to concentrate on
eating and breeding, fire ants multiply
expo nentially in such areas. Although
multiple q ueens are sm aller and weigh
less than queens that rule alone, they
produce a large r totlll of eggs. As a result,
an acre that migh t have 40 mounds of
single-queen fi re an ts mll support as
many as 400 mounds of multi-queen
ants. D ensi ties as high as 600 mounds
per acre h ave been docum ented in a
few areas. 'While th ere might be 20 mil­
lion ants in an acre of single-queen ter­
ritory, a multi-queen aue can have as
many as 200 million an ts.
M o re ants are mo re dangero us. Hants
from o ne mound happen upon a good
food sou rce- a family's picnic or a nest
of helpless quail h atchlings-they can
go back to their netwo rk of m ounds apd
"recrui t" millions upo n millions of
other ants. W ithin minutes, the qnar­
ry may be overcome by the insects.
Even though multi-queen fire ants
are slighdy smaller th an single-queen
ants, they may be ha rder to knock out.
As the an ts shar e food with on e anoth­
er, pesticide bait m.y travel quickly from
mound to mound , but it h as to reach
every queen in ord er to destroy the
m onnds. If even one q ueen o nrofhun­
dredssurvives, the mounds may rebound
after a pesticide trea ttnent.
T h e density, cooperatio n and tenac­
ity of multi-qneen fi re ants have forced
scientists and wi ldlife managers to
reconsider h ow these pests change the
ecosystem. "The impact studies done
Texas Parks &' Wildlife
41
Texas Parks & Wildlife August 1994 pp. 38-43
from the 1940s to the 1960s didn'trec­
ognize the m ulti-queen fire ants. Now
all that work has to be reevaluated," sa1d
Bastiaan M. D rees, an associate pro­
fesso r of entomology at T exas A&M.
"We're just at the foothills of that
effort."
Scientists first looked at how themul­
tiple-queen fire ants affected other
insects, including their cOllsins, the
native fire ants. In 1988 , a University
of T exas study concluded that multi­
ple-queen fire ants were replacing na bve
fire ants and then creating mound com­
munities that were six times as dense.
At about the same time, Vinson's staff
at Texas A&.c'\1 found that in areas where
there once had heen dozens of insects,
only one or two species remained after
an invasion ofthe multi-queen fire ants.
They cut species diversity by 70 per­
cent and numbers by90 percent. O ther
studies by Texas Tech University and
by the USDA yielded similar results:
the multi-queen tire an ts were deci­
rnating other jnsec[s.
They also may be endangering species
already threatened with extinction. In
1990, a rese arch er fOWld swarms ofants
foraging as much as 80 feetunderground.
The r esearcher I a cave specialist, never
had seen anything like it. H e asked the
Texas DepartmentofAgrimlture to find
out what was killing and canying off
Tooth Cave pseudo-scorpio ns, Bone
Cave harvestman spiders and other
species-some of which are on the
endangered species list ofthe U. S. Fish
and W ildlife Service. The predatory
swarms turned out to be fire ants fro m
multi- queen mounds.
and so on, up the food chain .
Wbile this idea makes sense to many
fire ant experts, it has been difficuJt to
prove. To do so requires trapping and
tracking animals in areas that don 't sup­
port them in numbers large enough to
make statistical ana lysis significant.
Becauseit is too difficult and too ex pen­
sive to study the impact fire ants have
on every species in every habitat,
'''~'''' ha t's
happening to insects
now may happen to larger
animals later. Scientists point
out that these insects form a
base upon which is built the
habitat ofall o ther plan ts and
animals, including humans. "Ants are
one ofthe solid foundations of the food
pyramid. If fire ants disturb that, the
effect will be su btle but profound," said
Les Greenberg, the A&M researcher
specializing in multi-queen ants. "Ifwe
don't Jook for effects , we probably
won't find them now. But then, years
from now, we all may wake up and find
dozens ofspecies have disappeared, and
th en trace that all back to the multi­
queen tire ant colony." In other words,
jf one insect species dies out, a food
source for a small mammal may dry up.
F ewe t sm all mammals may cu t down
on the populotion of predatory birds,
researchers have to fo cus on one species
or one type of animal in one specific
environment. ll1evitably, these efforts
involve a certain amountofhit-or-miss
risk.
One of the tirst efforts to quantifY
the effect fire ants have on large r ani­
mals was directed by Drees, in the
Rollover Islands, a string of low-lying
islets in East Galveston Bay. More than
a dozen ground- and sh.rub-nesting
waterbirds, including great hJue herons,
gTeat egrets and suowy egrets, n est on
the islands fi'omMarch to AUg1lSt. The
islands also are heavily infested with fire
ants. Drees and his researc hers treat­
ed some islands with pesticide and left
o thers untreated. During 1989 and
1990, they compared the nesting suc­
cess in treated areas versus that in
untreated areas. In the ant-infested
areas, Drees found tl,at the insects did
kill hatchl ings, especially during th e vul­
nerable time when the chicks have just
"pipped," or broken through their
shells. Fire ants completely wiped out
th e nests of some species that hatched
during the Jast half of the nesting sea­
son, from June on. Drees's study, how­
ever, did no t take in eo accountwhether
the ants cam e from mul ti-queen or sin­
gle-queen mounds.
Farther north, around Coll ege
Station, Texas A&M vVildlife and
Fishelles Professor Bart W ilson has been
trying to find out just how multiple­
queen colonies affect small wildlife.
Wilson and his graduate students found
W01'ket· ants ten.d Illrvae and puplle in Il colon)"
left, Dlwing the lllst det:f1de, scientists ba've dis­
covered multiple queenfi1'eonl tolonies tbatam­
l{fin up to 200 queen mus, as opposed to lbe
traditional single queen colonies tbot cQntain
011fy olle queen.
42
A'g<m 1994
~as Parks & Wildlife August 1994 pp. 38-43
I
I
Ground-nesting bints can be killed
}in ants that swann over the
hatching C&r1S dud the1lew4y batched
chicks. These eggs belong to the
threatened 1widish egret.
~y
that small animals react to fire ants as
ifthey were a slow- burning prairie fire.
When fire ants invaded the nests ofcot­
ton rats, pygmy mice or quail, the ani­
mals moved away. In another study of
four counties in northeastenl Texas,
Wilso n's srud ents found that there
were fewer roden~in<lreasinfested with
multi-queen colonies. This means less
prey for larger animals, and th at conJd
h ave a devastating effect down the line.
"We're not finding smue species
where we used to or in th e n LUnbers
that we used to," Wilson said. "I don't
doubt for a minute the people who say
fire ants ace driving out other species.
W e just don't have the da ta to prove
that yet."
Slowly, the datais begillning to come
in. The United States D epartment of
Agricnlture, the Texas D epartment of
Agriculrureand Texas Tech University
in Lubbock joined forces to srudy the
impact multi-queen fire ants had on the
wildlife on several private ranch es near
Victoria.
Researchers marked off 10 areas 400
to 600 acres in size. They grouped th e
parceJ.s into five pairs, treating One par­
cel ofeach pair with insecticide and leav­
il~g the other in its natura l state. T hen
they compared wildlife abundance in
the n'eated versns the untreated parcels.
In 1991 , the researchers found little dif­
ference in wildlife in the treated and
untreated areas. Burwhen they rettmled
th e second year , they fowld twice as
many 'luail in the treated areas, where
the Arridro insecticide had reduced the
fire ant population by 90 percent. They
were surprised by o ther find­
ings: there were twice asmany
deer fawn s in the treated
areas. T here was als o a sig­
nificantly larger number of
loggerhead shrikes, birds that
depend on iusects as a major
part of their diet.
"As biologists, we were amazed arhow
simple this seems to be,"saidLutz. "The
ants prey on newborn quail and deer
fawns . They eat insects that birds need
for food. Fire <lnrs make a trelnendous
difference in the ecosystem."
It's not difficult to get a little alarmed
about such results. Fire a.nts make for­
midable opponents. Don Wilson, a
Texas Parks and Wildlife progr am
coordinator for upland gam e, has seen
tl,e ants kill quail chicks in less than a
minute. "They get under the n atal
dmvn and sting all at once/' Wilson says.
"When th ey hit the chick, it was like
he was snake bit; he convulsed. I t only
took 30 seconds. " Trostle, ofth e T exas
Deparunenr of Agri culrure, said he
most remembers th e baby deer. "In th e
multi-queen areas, we find blinded
fawns. I t's pitifu\. Their eyes are white
from the sti ngs and they're crying," he
said. "T he fire ants are preying on every­
thing Ont there. They'te really chang­
ing our ecology."
At the same time that they evoke tl,ese
fan tastic images, researchers also warn
against panjc. Wilson said he hasn't
heard qua il on his fannnear Anstin since
L987. nBut that doesn't mean the fire
ants did it," hesaid. "Ther e areso m any
factors out there.
P erhaps the most ambitious attempt
to get a definitive picture of the fire ant
threat is the srudy sched ul ed to begin
this summer at Lake C onroe, near
Housto n. Research ers V in so n and
'Nilson have found a narurallaborato­
ry in a large traer of publicly owned
lan d free of pesticides. T he o ..ctis heav­
ily popnla ted with fire ants in monnds
that are diso·ibuted fairly evenly. The
area will be divided inro a checkerboard,
with ten sections 240 feet wide by 400
feet long. The team will trea t tl,e first
o'act with a pesticide such as Amdro or
Logic, then leave the next tractuntreat­
ed, alternating in this way through all
tl,e tracts. Then tlley will set a line of
live traps through th e plots. They will
then compare tl,e amoun t of wildlife
in the treated plots versus the nntreat­
ed plots.
"The problem with the small mam­
mal studies is that we haven 't caught
enough animals to nave significant
numbers," said Vinson. "We hope with
this srudy we'JI fi nally get tl,e numbers
th.ttell us what's going on. "
j)
'*
Heather Millar, formerly o[Houston, is a
ji-eelance writer based in Ne-J! Y07·k City.
Choke Canyon State Park o n the sho res o f 26,OOO-acre C boke
Canyon ReservoiJ' is one of the state's fin est COl'Op\e.'(es for camping,
fishing and enjoyrnentof nature. vVildlife isabundan [in the park's Calliham
and South Shore un its, and visitors enjoy dose looks at white-tailed
deer, javelinns, rurkeys, quail and a host of other birds. The park's bnTsh
country habitm is dominated by mesquite, blackbrush and cactus, with
wildflowers in springtime . Visitors can reserve t:ampsites arrent a large
family pavilion complete 'With kitchen and gym.nasium, ;]djaccnt w an
o lympic-sized swimm ing pool. \ lisiro\.U· park store for concessions and
souveni rs. Cho ke Canyon provides educaaonal and recreatio.ua l pro­
g ra ms fm park v:isi tors, schools, dubs and othe r groups. The park is
Loca ted between Th ree Rivers and T ilden on Stare Highway 72.
VISIT · CHOKE ·CANYON Call 512-786·3868 for information
or 512-389·8900 for reservations
Texrts p(frks &- WiWift
43