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) 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) /Cybister-tripunctatus-image.html

The Dytiscid Ctd. The Dytiscid swims by moving its back legs simultaneously, and when necessary they can fly. The Dytiscid swims by moving its back legs simultaneously, and when necessary they can fly. (CSIRO 2004) (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. 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. 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 # of Traps Times Checked Lake Romeyn 214 Lake Romeyn (Shallows) 214 Path Pool 114 Landfill Pool 214 Vernal Pool NOTE: All traps (except VP1) were baited with sardines. Trapping occurred from May 5 through May 22.

Tank/Prey Layout Tank # # of Dytiscids Prey 11 3 Small (10mm) Wood Frog Tadpoles (Rana sylvatica) 21 2 Damselfly Larvae (Zygoptera), 1 Earthworm 31 1 Medium (20mm) bullfrog tadpole 41 1 Large (25mm) Green Frog Tadpole (Rana clamitans) 52 3 Small (10mm) Wood Frog Tadpoles, 1 Earthworm 61 1 Pickerel (45mm) (Esox niger) 7 (cover) 1 3 Small (10mm) Wood Frog Tadpoles

Predation Results Tank # # of Dytiscids Predation 11 All three Woodfrog Tadpoles consumed within one day 21 The two Damselfly Larvae consumed within one day. Earthworm consumed the following day. 31 The 20mm Bullfrog Tadpole remained unharmed for 4 days. 41 The 25mm Green Frog Tadpole remained unharmed for 4 days. 52 One Wood Frog Tadpole consumed on the first day. Day after next, one more tadpole and an earthworm eaten. 61 The Pickerel remained unharmed for 4 days. 7 (cover) 1 All three Woodfrog Tadpoles consumed within one day

Correlation Between Consumption and Size As Figure 1 displays, the Dytiscids can only tolerate prey up to a certain size. Figure 1

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. 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 1.) CSIRO, “Family Dytiscidae.” July 2, 2005.mhttp:// Dytiscidae/index.html 2.) Mcleod, Robert, “Vertical Diving Beetle.” November 11,