Stonefly Life Cycle: A UtahOTF Pictorial
Fortunately for us, the stonefly is a fairly common insect on most Utah rivers and streams. While there are numerous types of stoneflies that we differentiate primarily on a visual basis, it holds true that they all follow the same basic life cycle.
The stonefly life cycle can be broken down into 3 fundamental stages:
- Eggs which are also known as ovum.
- Nymphs which are also known as larva.
- Adults which are simply known as adults.
Life for the stonefly begins in the egg. When the adult female deposits her eggs in the water, the egg sinks to the bottom and with any luck becomes lodged in the riverbed. The eggs struggle to avoid being washed downstream by means of a sticky coating that encapsulates the egg, or by attaching themselves to bottom structure via small projections on the outside of the egg case. Once securely attached, the egg begins to mature. The inevitable success and duration of the maturation period is dependent upon water conditions and the type of stonefly. It can take as little as a few hours or as much as a few months.
After emerging from the egg, the stonefly begins the nymphal phase of its life. Depending upon the type of stonefly, this phase can last anywhere between 1 and 4 years. During that time, a stonefly will molt it's exoskeleton as many as 25 times as it grows. Again, the number of "molts" is type dependent. Quite often you can see theses discarded exoskeletons floating downstream!
Emergence finally occurs after sufficient maturation. Most stoneflies emerge under the darkness of night as they crawl out of the water onto nearby banks. They then attach themselves to a blade of grass or some other handy object. It is at this point when the stonefly will begin to work itís way out of the nymphal casing to enter the adult world.
Life as an adult is short and basically consists of mating and laying eggs. Male stoneflies typically live no more than a few days and the females slightly longer. Mating stoneflies attract one another by beating their abdomen on blades of grass, leaves or similar objects. The vibrations are actually transmitted to members of the opposite sex through the objects! Once females have mated, they will cease sending off vibrations.
Adult females will deposit their fertilized eggs into the water in one of two ways. She will either release their egg cluster above the water from the air, or alternately, crash into the water and shake the eggs loose. Both of these techniques are readily observable!
The following images track the lifecycle of the stonefly from the nymphal stage through adult. Please enjoy!