Download Foraging Habits of the Dytiscid Beetle

Foraging Habits of the
Dytiscid Beetle
Peter Taylor
Seppi Colloredo-Mansfeld
The Dytiscid Beetle

Dytiscid, or vertical diving beetle,
is one of the most commonly
encountered, and one of the
most important aquatic insects
found in the bodies of water
around Groton. These
predaceous beetles are a major
predator in vernal pools and
lakes. (CSIRO 2004) They have
been know to attack a wide
variety of small aquatic animals.
(CSIRO 2004) Generally, the
beetle is small to medium sized
(20 mm), though they have been
know to grow to 35 mm long.
(CSIRO 2004)

http://www.anbg.gov.au/cpbr/WfHC/Dytiscidae
/Cybister-tripunctatus-image.html
The Dytiscid Ctd.



The Dytiscid swims by moving its back legs simultaneously, and
when necessary they can fly.
(CSIRO 2004)
Both Larvae and Adults prey upon a wide variety of small
aquatic life. The adults eat through a mouth. Larvae have long
jaws which they use to suck fluids out of prey.
(CSIRO 2004)
The beetle needs to surface in order to breathe. They can store
oxygen underneath their wing covers to increase their time
underwater.
(CSIRO 2004)
Aquatic Trap Setup
Trap
Location
Lake Romeyn
Lake Romeyn
(Shallows)
Path Pool
Landfill Pool
Vernal Pool 1
# of Traps
2
2
Times
Checked
14
14
1
2
10
14
14
3
NOTE: All traps
(except VP1)
were baited
with sardines.
Trapping
occurred from
May 5 through
May 22.
Tank/Prey Layout
Tank #
# of Dytiscids
Prey
1
1
3 Small (10mm) Wood Frog
Tadpoles (Rana sylvatica)
2
1
2 Damselfly Larvae (Zygoptera), 1
Earthworm
3
1
1 Medium (20mm) bullfrog
tadpole
4
1
1 Large (25mm) Green Frog
Tadpole (Rana clamitans)
5
2
3 Small (10mm) Wood Frog
Tadpoles, 1 Earthworm
6
1
1 Pickerel (45mm) (Esox niger)
7 (cover)
1
3 Small (10mm) Wood Frog
Tadpoles
Predation Results
Tank #
# of Dytiscids
Predation
1
1
All three Woodfrog Tadpoles
consumed within one day
2
1
The two Damselfly Larvae
consumed within one day.
Earthworm consumed the following
day.
3
1
The 20mm Bullfrog Tadpole
remained unharmed for 4 days.
4
1
The 25mm Green Frog Tadpole
remained unharmed for 4 days.
5
2
One Wood Frog Tadpole consumed
on the first day. Day after next, one
more tadpole and an earthworm
eaten.
6
1
The Pickerel remained unharmed for
4 days.
7 (cover)
1
All three Woodfrog Tadpoles
consumed within one day
Correlation Between Consumption
and Size
number of prey consumed
Prey Consumed Relative to Size
10
8
6
Series1
4
2
0
0
20
40
60
size of prey (mm)
Figure 1
As Figure 1 displays, the Dytiscids can
only tolerate prey up to a certain size.
Affect of Cover on Predation
One tank contained a large amount of aquatic
growth, acting as shelter for the three wood frog
tadpoles we placed in the tank with the beetle.
When we checked the tank the next day, we
found all three tadpoles were gone. In the
control tank, the beetle took the same amount
of time to consume the three wood frog
tadpoles placed in clear water. This suggests
that cover has little to no affect on the beetle’s
foraging habits.
Mating effects on Foraging Strategies

With the option to mate, the beetles are less focused on
capturing the prey and tend to spend more time
breeding than hunting. We placed a male and a female
Dytiscid in Tank 5 to see how it would affect their
foraging strategy. Consequently, the 3 tadpoles in the
tank were not all consumed within a day like the other
two tanks with small tadpoles, but instead only 2 of the
tadpoles were eaten over 3 days. When observed, the
two beetles would most often be mating rather than
chasing the prey. The presence of females therefore
inhibits foraging productivity for these beetles.
Conclusion
The Dysctid beetle’s prey base is limited by the size of the
animals being hunted. We found that the agility of the
prey, particular species, and varying conditions of the
habitat did not affect the foraging strategies of the
beetle. When placed in tanks with larger tadpoles and
the fish, the beetle would attack the tadpole or fish,
who would not avoid the attack, but be unable to
successfully consume the animal. The smaller tadpoles
would avoid attack at all costs, however, they were just
as easily eaten as the small earthworms we placed in the
tanks.
Conclusion Cont.

The Dytiscids, because of their varying prey
base, are a successful species in the Northeast
and are prevalent in most bodies of water.
Although the size and species of prey they
compete for are a popular kind of food, they
can easily hunt down prey with their apt hunting
abilities.
Works Cited
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1.) CSIRO, “Family Dytiscidae.” July 2,
2005.mhttp://www.anbg.gov.au/cpbr/WfHC/D
ytiscidae/index.html
2.) Mcleod, Robert, “Vertical Diving Beetle.”
November 11, 2007.
http://bugguide.net/node/view/86834