Hunters in the Pond, Part 1 – Terry Thormin
The young cutthroat trout swam warily through the water. At 8 cm ( just over 3“) long it was still quite small, even by fresh water standards. Cutthroats that stay in smaller fresh water ponds all their lives rarely get over 40 cm (16”) long and two pounds in weight, whereas saltwater populations can weigh up to twenty pounds. The cutthroat was looking for food, any insects would do. But right now it was not having much success. To avoid being taken by a kingfisher or a great blue heron it had kept to the centre of the pond and was hunting in deeper water, but lack of success had driven it in closer to shore. It was now searching amongst the emergent rushes along the shoreline.
It never even saw what hit it. Suddenly from the leaf litter at the bottom of the pond powerful front legs shot out and grabbed it around the middle and heavy spines punctured through its scales, holding it fast. It jerked violently as needle-like mouthparts pierced through its scales to its very core. The pain of the toxic digestive juices was overwhelming but all its struggles were for naught. As digestive enzymes turned organs and muscles to soup, its struggles became weaker and weaker until finally the life slipped from its body.
Giant Water Bug with Cutthroat Trout
The Giant Water Bug feasted for a full day before it was satiated. It was at its penultimate stage and it now had the body reserves it needed to go through the final molt to adulthood. It released the cutthroat which floated to the surface and became food for scavengers. It searched out a place close to shore in amongst the floating vegetation where it could stick its breathing tube out of the water while its old skin split down the middle of the back and the new adult, complete with wings, emerged. Even as the ponds top insect predator, this was a dangerous time for the giant water bug. Its new exoskeleton was soft and offered no protection, and even much smaller insects could attack and kill it at this stage. It would be several hours before its exoskeleton was hard enough to give it proper protection.
Giant Water Bugs are just one of many types of insect predators that are found in fresh water bodies. They are ambush predators, sitting amongst dead leaves and other debris at the bottom of ponds waiting for something to come close enough to grab. They are superbly camouflaged for this purpose. As well as taking other insects and small fish, they have been known to kill frogs, turtles and even snakes. Their bite is considered to be one of the most painful of all insects, and has earned them the name toe-bitter. The largest North American species is Lethocerus americanus, and the biggest of individuals can get up to 65 mm (more than 2 ½”) long. Females of this species, and others in the genus, lay their eggs in a mass on emergent vegetation. Females of other genera lay their eggs on the backs of the males. This affords the eggs better protection from predators while both aerating them and keeping them moist. In the tropics some giant water bugs can get up to 12 cm or more than 4 ½ “ long. There are about 150 species worldwide.
Adult Giant Water Bug
Predaceous diving beetles are another family of ferocious predators found in fresh water bodies. These beetles range in size from about 1 mm to over 44 mm (0.05 to 1.75”) in length. Unlike Giant Water Bugs they are active hunters, often searching the bottoms of ponds for their prey which mostly consists of other insects, tadpoles and small fish for the largest of species. Adult beetles are air breathers and have to regularly come to the surface to get more air. When they dive under the water they carry a reserve layer of air under their wings alowing them to stay submerged longer.
Predaceous Diving Beetle
The larval stage looks quite different from the adults and these are called water tigers. Like the adults the larvae are fearsome predators with needle like jaws. There are about 4,000 species worldwide.
A third group of aquatic predatory insects is the back-swimmers. This is another family of true bugs, and all species are active hunters. Unlike other aquatic insects they spend their lives swimming upside-down, hence the common name. Like the giant water bugs and predaceous diving beetles they swim with their back legs which are modified for that purpose. In the backswimmers those legs are exceptionally long and look very much like oars. These bugs are primarily insect eaters although the largest of species, which can get up to 2 cm (0.8”), will take small tadpoles and fish. They regularly come to the surface of the water for air, which they carry with them as a silvery sheen on the under surface of the abdomen. They are often seen hanging upside down at a 45 degree angle from the under surface of the water, ready to swim quickly downward if danger threatens or they see potential prey. There are about 400 species worldwide.
All three of the above families of insects have one thing in common, as adults they have wings and can leave the water and fly. They use this primarily as a dispersal mechanism. Most flights happen at night when the insects use the moon for navigational purposes. If you use the moon for navigational purposes, as long as you keep the moon in the same relative position in the sky and you do not travel for a long period of time, you will travel in essentially a straight line. Unfortunately when insects try do this in the presence of bright lights they end up flying in an ever diminishing spiral around the light until they come in contact with an immoveable object like a wall or the light itself. I am sure that everyone has seen the results on the wall behind their porch light or below a particularly bright street light are at the very bright lights at many gas stations. Inevitably this ends in the premature death of many insects. It has also earned the giant water bug another colloquial name, the electric light bug.
There are three other groups of aquatic “bugs” I would like to write about, actually two insects and a spider, but before this blog gets way to long, I will quit here and save the others for a second blog.
Death Stalks the Pond
Beneath the pond, amidst debris,
the water bug waits patiently.
She hides amongst the leaves so well
her presence is so hard to tell
The fish swims by unknowingly,
until it’s hit most forcefully.
Spined legs dig deep and hold it tight,
and needled mouthparts start to bite
Death stalks the pond
As on its flesh the bug does feed,
the fish provides what the bug needs,
to grow and molt and finally be,
an adult, its true destiny.
She finds a male, mates and with tact
lays rows of eggs upon his back.
And every egg has life within,
another cycle to begin.
And life goes on
©Terry Thormin July 4, 2012