TWO AQUATIC INSECTS OF THE GREAT SALT LAKE;
THE BRINE FLY AND CORIXID BUG (WATER BOATMAN)

  Index:  Why aren't there any vertebrates that live in the lake?
              What are the common invertebrates in the lake?
              Brine Fly
              The life cycle of the Brine Fly
              Corixid Bug
              The effects of salinity on Corixid Bug populations
              For further information on these aquatic insects

WHAT ARE THOSE FLIES ON THE BEACH AND WHY DON'T WE GET RID OF THEM?
 
     The most visibly obvious invertebrate that inhabits the lake is probably the brine fly. Visitors to the lake, whether a 

first time or local, walk away with a vivid image of the huge, coal black clouds of flies that inhabit the salty shores.  Many

leave without desire to return because of these "noxious insects;" However, there is a Utah State Park sign on

Antelope Island that assures visitors that the masses of sometimes annoying flies are imperative to the ecological "plan" of 

the lake.  Astute and sensitive observers can connect the flies to the rest of the lake's system of existence -- that is if one 

does not follow the conditioned trail of imagery in history that characterizes places like saline lakes as wastelands.  As Ella

Sorenson puts it in the voice of the lake itself: "Do you call my waters dead because you expected fish and found none?  An

abundance of plants and animals live within and around my briny depths.  If not life, what do you call brine shrimpbacteria,

algae, brine flies?"   So a shift in thinking from traditional wilderness imagery (green trees, mountains, and mammals) to one

that celebrates dryness, adaptation, and specialization is necessary and important if we are to understand and value places

like the Great Salt Lake that have been traditionally neglected due to their "non-traditional" characteristics.

WHY AREN'T THERE ANY VERTEBRATES THAT LIVE IN THE LAKE?
 
     The salinity of the Great Salt Lake poses extreme physiological stresses on the organisms that live in and around the

lake.  Vertebrates like birds and voles inhabit areas surrounding the lake like fresh/brackish marshes, rocky outcrops, the

salt playa, and dunes.  Many of the vertebrates have adapted to excessive salts in their diets.  For example, California gulls

excrete excess salt from their diet of brine shrimp, brine flies, and algae through  their salt secreting adapted nostrils;

However, organisms that live in the lake must regulate salt levels more efficiently and vigorously than

the part time residents like birds.  Most vertebrates such as fish have not evolved mechanisms to deal with so much salt and

therefore, none inhabit the lake. 

WHAT ARE THE MOST COMMON INVERTEBRATES?  
 
 

The Brine Fly:   
     
     There are two identified species of brine flies: Ephedra  

cinerea and a larger species E. hians.  E.  cinerea is far  

more abundant in the south arm outnumbering  its larger  

counterpart by 100:1 possibly due to the  differences in  

salinity between the North and South arms.  The flies do not  

prey on humans and/or  other mammals and birds – instead  

the adults and their larvae feed on bacteria   and algae that  

grow on the  surface of rocks and wood on the floor of the  

lake or near the shoreline.   In this way, the brine fly is  

important to the lake in that the flies reuse massive amounts  

of organic "waste" from the lake.

 
  The Life Cycle of the Brine Fly:

     The adult flies are 3-6mm in length and their average life span is 3-5 days.  Egg laying is continuous through the summer

and females typically lay 75 eggs – which are laid on or near the surface of the water (females lay eggs under water by

“walking” underneath with a bubble of air surrounding her) then the eggs hatch into long cylindrical larvae that consume

large quantities of algae and decaying organic detritus in the lake. The larvae are distributed throughout

the lake at different depths and build up by drifting in to algal reefs.  On these reefs of algae, the larvae 

survive completely submerged and receive dissolved oxygen from the water that passes through their tracheal gills.  Lab

observation shows a high mortality rate during pupation, the time when the larvae metamorphose and develop wings and

leave their pupal cases behind.  When they emerge they rise to the surface enclosed in an air bubble and are then

transported to shore by the wind.
 

Wind direction and velocity have a large impact on  

distribution of brine flies throughout the lake and help to  

create the long,  dense windrows of pupal cases and huge  

clouds of flies on  the shore as shown in this photo. This  

whole life cycle lasts 3-4 weeks.  Since the fly's complete 

life  cycle depends on the growing conditions of the lake, it  

seems that the  lack of numbers in the north arm may be  

indicative of the  disruption of natural salinity because of the  

division of the  lake by railroad in 1959. 

 

 
 
 
Corixid Bug (water boatmen):
     The earliest specimens of the predatory insect in the family Corixidae (water boatman) were collected in the south arm of

the lake in 1926 by a scientist named Allen.  Later, Woodbury (1936) reported that no other invertebrates besides brine

shrimp and brine flies existed in the lake; However, about ten years ago at the Silver Sands Marina (South arm) E. Rawley

collected adult Corixids that were identified as Tricorixia verticalis Fiber.  Corixids are predatory and prey on brine shrimp,

Artemia salina, as well as the larvae of the two species of brine flies. The effect of this predation on the shrimp and the

brine fly population is under investigation by the Utah Division of Wildlife Resources in cooperation with the United States

Geological Society.  For research updates on the Great Salt Lake Ecosystem Project see:

http://www.nr.state.ut.us/dwr/GSLECO.HTM#university.  At one time, it was thought that the bug reproduced in the

fresher marshes and migrated in as adults.  Winget, however reported collecting immature and adult Corixids from several

areas in the south arm and so it seems that these water boatmen are true inhabitants of the lake.

 
drawn by Nghia Ngyen, 1998
These bugs belong to the family Corixidae (commonly  

called water boatman) and constitute the largest group of  

water bugs in north America with over one hundred  

species.  Water boatman are free swimming bugs  

and have modified scoop shaped forelegs and oar like  

hind legs with swimming hairs.  In a habitat like the Great  

Salt Lake which is generally oxygen poor, the Corixids  

surface regularly for air but also have a physical gill called   

a plastron which stores air and ventilates as the bug rows  

its oar like legs. In more oxygen rich environments the bug  

can stay submerged for longer periods of time. 
 

THE EFFECTS OF SALINITY ON CORIXID BUGS:
 
     When the lake water was more dilute, such as in the fall of 1998 due to an abnormally high amount of precipitation for

the year, high populations of this bug were found by students of Westminster in the Farmington Bay arm of the lake which is

South of the north Antelope Island causeway.  A sample of the lake water showed that the salt concentration was 3.7%.

Similarly, A rise in water level that occurred from 1960-1989 decreased the Great Salt Lake's salinity from more than 30% in

both the northern and southern basins to 17% salinity in the northern basin and only about 6% salinity in the southern

basin.  These changes in salinity and water level had profound ecological repercussions.   For example, the lower salinity

level made it possible for this predacious water bug, Trichorixia verticalis, to increase their numbers in the lake.  This insect

preyed extensively upon the previously dominant brine shrimp, Artemia franciscana.  A marked change in the composition of

phytoplankton was also a consequence of this increased inflow of runoff.  Once dominated by salt tolerant algae such as

Dunaliella salina and D. vividis, the phytoplankton gradually changed as the lake became diluted so that opportunistic

forms, such as Nodularia spumigena, had a chance to flourish (Williams).
 
For Further Reading See:

The Division of Wildlife Services Great Salt Lake Ecosystem Project web site for up to date research

The Salt Lake Tribune Archives article on dioxin pollution and its effects on the lake
 
 

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REFERENCES

Gwynn, J. Wallace, ed.  Great Salt Lake; a Scientific, Historical, and Economic Overview.

     Utah Geological and Mineral Survey, 1980.

Mccafferty, Patrick W.  Aquatic Entomology; The Fisherman's and Ecologists' Illustrated Guide

     to Insects and Their Relatives.  Boston: Science Books International, 1981.

Sorenson, Ella.  Seductive Beauty of Great Salt Lake; Images of a Lake Unknown.  Salt
 
     Lake City:  Gibbs-Smith, 1997.

Williams, David Williams. "What Future for Saline Lakes?"  Environment. Nov 1996 v38 n9 

     (p12).