Mayflies from the family Baetidae are this month’s ‘bug of the month’. Commonly known as blue winged olives by fly fishermen, Baetid mayflies are small (<10mm) and can be extremely prolific. In addition, they grow rapidly and can have multiple generations within a year (known as multivoltine). This means that you can see adult Baetid mayflies during most of the year although they are especially apparent during the winter in early spring when few other bugs are hatching.
Photo Credit: TroutNut.com
Baetid mayflies are exceptionally adept at colonizing new habitat. They are extremely good swimmers (for a bug) and are known for undertaking what is known as behavioral drift. Behavioral drift is a strategy where macroinvertebrates enter the flow of the river voluntarily to seek out new habitat. Short life cycles, excellent swimming ability, and the propensity to undertake behavioral drift allow them to settle new habitat like when high flows inundate floodplains.
They are often the first to colonize a new area due to their swimming skills and their preference for shallow, slow water. These newly formed areas grow algae very well which is the primary food source for Baetid mayflies. They can often exploit newly formed habitat within a few weeks and live their entire life cycle within 12 weeks before other bugs get a chance to settle in an area. Seasonal inundation of floodplains are extremely important to Baetid mayflies success. Juvenile salmon have evolved to depend on the seasonal inundation of floodplains because of the presence of Baetid mayflies, which they eat for food.
Chris Laskodi, M.S., Fish Ecologist – Yurok Tribal Fisheries Department
Chris serves as the fish biologist/ecologist for the Trinity River Restoration Program in the program’s Science branch. Chris has worked on the Trinity River since 2015, previously serving as a fish biologist for the Yurok Tribe and a fisheries technician for the US Fish & Wildlife Service. Chris holds a B.S. in Wildlife, Fish and Conservation Biology from the University of California, Davis and a M.S. in Aquaculture/Fisheries from the University of Arkansas at Pine Bluff. In his free time, Chris enjoys taking friends and family fishing on one of the many watercraft available to him.
Dicosmoecus (dee-co-smee-cus) caddisflies are better known by the common name ‘October caddisflies’. These caddisflies are notable for there extremely large size (1-2 inches), their concentrated emergence window (October), and their abundance especially in streams containing anadromous fish. These characteristics make it one of the most important hatches to not only fly-fishermen, but to wildlife such as birds as well.
Dicosmoecus like other caddisflies have three life stages: larvae, pupae, and adult. Larvae build cases out of small rocks which serves as protection and their housing. They drag these cases around while foraging for food, mostly algae and detritus. Dicosmoecus are especially notable by the large distances they can cover (up to 25 meters per day) to forage (Resh et al. 2011).
They continually grow and have to build new cases as the old ones become too small. After molting five times (called instars), they attach their cases to the underside of rocks and began to pupate. After about a month of pupating, they cut a hole in their case and swim to the surface before shedding their exoskeleton one more time and becoming adults.
Caddisflies, unlike mayflies, will live for several weeks while they seek out a mate. You will often see them active at dusk and just after sunset. Keep a look out for the large moth-like bugs during sunset for the next few weeks.
References
Resh, V.H., M. Hannaford, J. Jackson, G.A. Lamberti, and P.K. Mendez. 2011. The biology of the limnephilid caddisfly Dicosmoecus gilvipes (Hagen) in Northern California and Oregon (USA) streams. Zoosymposia 5:413-419.
Images courtesy of Red’s Fly Shop and Troutnut.com
Chris Laskodi, M.S., Fish Ecologist – Yurok Tribal Fisheries Department
Chris serves as the fish biologist/ecologist for the TRRP in the program’s Science branch. Chris has worked on the Trinity River since 2015, previously serving as a fish biologist for the Yurok Tribe and a fisheries technician for the US Fish & Wildlife Service. Chris holds a B.S. in Wildlife, Fish and Conservation Biology from the University of California, Davis and a M.S. in Aquaculture/Fisheries from the University of Arkansas at Pine Bluff. In his free time, Chris enjoys taking friends and family fishing on one of the many watercraft available to him.
You may have noticed a rather large insect fluttering down the river during the months of September and October. These insects are mayflies from the family Isonychiidae (eye-son-nic-ee-uh-day) (known in the fly-fishing community as Mahogany Duns or Slate Drakes). Mayflies are unique in that they have two adult stages in their lifecycle while all other insects have one.
Isonychiidaemayflies usually live an entire year in the river as nymphs before swimming to the edges of the river, crawling out of the river on a rock, and emerging into their sub-adult stage. As adults, they typically only live for a day or two as their only job is to mate, lay eggs, and then die. Isonychiidae mayflies are noted for their large size compared to other mayflies and for their unique swimming ability. They are very adept swimmers and use their swimming prowess to capture their prey. They also have fine hairs on their forelegs which trap algae and other detritus which they then consume. The nymphs are a very strange looking (compared to other mayflies) and are readily identifiable by their elongated shape and ‘racing-stripe’ down their backs. Looking closely, the hairs on their forelegs become readily apparent and they are very easy to identify for any aquatic entomologist.
Isonychiidae mayflies are unique to the Trinity River with other populations scattered across northern California. The nearest population is found in the Pit River, but are rare there. The population in the Trinity River seems to be thriving and right now is the best time to see both the nymphs and adults. Look for the nymphs along the streambanks where they will look like small fish darting between the rocks. You will notice their shed exuviae (exoskeletons) attached to rocks. Adults can be found in the early afternoon fluttering in the air above the river. They seem to be more common in the area between Junction City and Cedar Flat.
Chris Laskodi, M.S., Fish Ecologist – Yurok Tribal Fisheries Department
Chris serves as the fish biologist/ecologist for the TRRP in the program’s Science branch. Chris has worked on the Trinity River since 2015, previously serving as a fish biologist for the Yurok Tribe and a fisheries technician for the US Fish & Wildlife Service. Chris holds a B.S. in Wildlife, Fish and Conservation Biology from the University of California, Davis and a M.S. in Aquaculture/Fisheries from the University of Arkansas at Pine Bluff. In his free time, Chris enjoys taking friends and family fishing on one of the many watercraft available to him.
If you’ve been lucky enough to spend time on the Trinity River lately, you will notice a plethora of brassy-green colored dragon flies hovering above the river fervently darting to and fro. The species you are most likely viewing is the common green darner Anax junius. Common is in its name, and that is certainly the case, for this species of dragonfly is the most common and abundant throughout North America. The remainder of its common name, Darner, is given due to its resemblance to a darning needle a blunt-tipped larger needle used for repairing holes or tears in coarse knitted cloth.
Dragonflies need water to reproduce. In the summer or early fall, common green darners seek riparian areas with slow water so they can mate and lay eggs in water-bound plant material. The female and male mate in an expertly posed “mating wheel” position – where the two are connected at their reproductive centers, the head of the female with the base of the male’s abdomen. The female’s abdomen is wrapped under the male so they can fly through the air, sometimes for several minutes. The female then unwraps her abdomen and lays eggs into the water while still attached to the male.
A female common green darner (left) in tandem position with male (right) deposits eggs. Ken Slade, Source: nps.org
Eggs hatch into macroinvertebrates (tiny aquatic larvae) after about a week incubation period and then go through upwards of a dozen nymphic molts eating aquatic insects, small fish and even tadpoles as they grow. At the end of the transformational nymph stage, Anax junius, emerges from the water to undergo metamorphosis into a dragonfly from a crack in the exoskeleton.
Common green darner aquatic nymph. Douglas Mills. Originally posted by the National Park Service.
Once the wings are developed enough to fly the darner becomes a ravenous forager eating mosquitos, midges, flies, wasps, moths and other flying insects. This dragonfly species has two different population types, resident and migratory. Residents remain in the general area from which they emerge. For residents in the north, the adults mate and lay eggs in late July to August. The resulting offspring hatch and develop to immature dragonflies and then overwinter when temperatures drop.
Adults that migrate tend to arrive in the northern regions in the spring before any of the residents emerge. Migratory adults mate and lay eggs in June. The migratory dragonfly’s development stage is less than that of the resident variety (3-5 months versus the 11 months of the resident) and they do not overwinter as residents do.
Common green darner’s in September on the Trinity River. James Lee, Trinity River Restoration Program
What are they and why are they important to river ecology?
Benthic: bottom-dwelling
Macro: see with the naked eye
Invertebrates: animals without backbones
Most of the life in rivers on any given day of the year are the small creatures that live out of the direct force of the river’s current, either attached to the rocks or wood, in spaces underneath or between pieces of gravel, or burrowed into silt. These animals include mussels, snails, worms, crayfish, and aquatic mites. But among all types of aquatic invertebrates, one class of animals stands out as the most diverse and complex – the insects.
An important term in river ecology is “benthic macroinvertebrate”, which refers to bottom-dwelling (benthic) animals without backbones (invertebrates), that you can see with the naked eye (macro). Ask a fly fisherman what trout and steelhead eat, and they’ll probably tell you salmon eggs if they’re available, sometimes other fish, occasionally snails, worms, grasshoppers or ants that fall into the stream, and with most frequency aquatic insects. Aquatic plants and algae photosynthesize energy from the sun. These plants then feed aquatic insect which in turn become an important energy for fish. Many insects have specialized mouthparts and behaviors to scrape algae and diatoms from rocks. Others feed themselves by shredding detritus (organic material that collects in rivers), or by straining food particles from the river’s flow, or by attacking and consuming other invertebrates.
Salmonid lifecycle and feeding
The mouths of small salmon fry are very small, and when their nutrient sac is no longer providing food prime food sources are plankton such as Daphnia (which could be considered “micro” invertebrates), small insect larvae such as chironomids (better known by their common names as midges or gnats) and young mayfly larvae such as baetids (known by fly fishermen as “blue-winged olives”).
Above, a chironomid larvae. Small and soft bodied, with generations as short as three weeks, this family of invertebrates rapidly colonizes seasonally flooded areas and provides excellent food for salmon and steelhead fry, as well as larger fish.
A larval giant salmonfly These insects live for three years in the river before metamorphosing into adults. While growing, they mainly eat detritus (organic material that collects on the bottom of the river). Image credit: troutnut.com
An adult giant salmonfly (Pteronarcys californica) A large stonefly that inhabits the Trinity River. On the Trinity River, these insects ‘hatch’, or metamorphize into adults in the spring. Image credit: Google.com
Older fish, the size of trout or steelhead, readily eat the larvae of larger insects such as caddisflies and salmonflies. Most aquatic insects are very small when they hatch from their eggs, and grow into progressively larger individuals after shedding their exoskeletons – a process called ‘molting’. Each growth stage is called an ‘instar’, and as they grow, each instar provides different sizes of food for different sizes of fish. After a range from a few weeks (for chironomids) to a few years (for some stoneflies and caddisflies) the insect pupates (similar to a caterpillar in a cocoon) and metamorphoses into a winged adult. Most of these adults are short-lived. Mayflies and stoneflies, for example, don’t even have functional digestive systems. They only live long enough to mate and deposit eggs in suitable locations along a stream.
A larval October caddis with a case made of stones glued together. While larger fish may eat these insects case and all, the high proportion of inedible material deters predators from eating them. October caddis generally spend two years in the river before they metamorphose into adults. They graze on algae and diatoms that cover rocks, but may also be observed feeding on dead salmon. Photo Credit: inaturalist.com
An adult October caddis (Dicosmoecus spp), a large caddisfly that lives in the Trinity River. As their name suggests, these caddisflies metamorphose into adults in the fall, when they lay the eggs for the next generation. Photo credit: troutnut.com
A larval baetid (blue-winged olive) mayfly. Although this photo was taken in Montana, similar species inhabit the Trinity River. Baetids are generally multi-voltine (have multiple life cycles per year), and this, coupled with their small size, makes them ideal food for salmon and steelhead fry. There are over 1,000 species of Baetids worldwide, and they have a variety of feeding habits, but are generally good swimmers and move around the river bottom feeding on that algae and diatoms that grow on rocks. Photo Credit: Encyclopedia of Life
A male Baetis (blue-winged olive) mayfly. Baetid mayflies are common in dam-regulated river reaches. These mayflies can hatch spring through fall, and even sometimes in the winter. Photo credit: troutnut.com
Macroinvertebrates and stream health
Many aquatic insects have very specific requirements for water parameters such as maximum temperatures, minimum dissolved oxygen, turbidity, pH, and salinity. These requirements make benthic macroinvertebrates very good bioindicators of stream conditions. The orders Ephemeroptera (mayflies), Plecoptera (stoneflies), and Trichoptera (caddisflies) are famous for requiring cold and clean water to thrive. In contrast, Chironomids, which belong to the order Diptera along with common houseflies, vary in their requirements depending on the species.
Stream ecologists can collect a sample of benthic macroinvertebrates and identify the species in the sample. In turn, the insects captured can then tell them about the condition of the stream. For example, if the sample contains a high proportion of individuals in the orders Ephemeroptera, Plecoptera, andTrichoptera, this indicates that the water quality is high. If the sample contains mostly species that live out their life cycle in just a few months, such as many species of Baetis and Chironomidae, this indicates that the water quality may change significantly between seasons. If the sample contains many species that have multi-year life cycles, such as salmonflies and October caddis, this indicates that water quality remains high throughout the year on a consistent basis.
The next time you visit the Trinity River, look around for aquatic macroinvertebrates. You might see cased caddisflies clinging to small cobbles. Turn one over, and you are likely to see mayfly larvae clinging to the bottoms. Look for the shed exoskeletons of stonefly pupa on branches and stems near the water’s edge. Look further to see if you can observe a trout or steelhead sipping adult insects off the surface as they lay eggs and complete their cycle of life.
James Lee grew up near Redding, Ca, but his heart has always been in The Trinitys, where he chased tadpoles, salmon, deer, and gold nuggets for much of his youth. This love of the outdoors turned into an interest in managing fish, wildlife, water, timber, and other natural resources.
