Meghan Hodges
Fishfly larvae are an important part of the food web, eaten by many fish, and are also used as bait in fishing. They are also used as bioindicators as they are sensitive to water pollution and are large enough to be assessed in the field. Some fishfly larvae are more sensitive to pollution than others. For example, dragonflies tend to be more sensitive to pollution than damselflies. Mayflies are also very sensitive to pollution and their absence in a stream can signal a problem. Caddisfly larvae are also sensitive to pollution and are used in monitoring water quality.
| Characteristics | Values |
|---|---|
| Fishfly Larva Characteristics | Fishfly larvae have 3 pairs of jointed legs in the upper part of their body, with each leg tipped with a tiny, 2-parted pincer. They also have several fleshy filaments extending from the sides of their abdomen and large pincer-like mouthparts. They look similar to their cousins, the hellgrammites, but lack cottony or hairy gill tufts along the abdomen and have 2 short, fleshy tails at the hind tip. |
| Sensitivity to Pollution | Fishflies are sensitive to pollution and are used as bioindicators of water quality. They cannot tolerate even small-scale pollution and will not be present in such environments. |
| Habitat | Different species of fishfly larvae prefer different aquatic habitats. Some prefer slow-moving, detritus-littered waters, while others require clearer, faster-flowing, and better-oxygenated streams. They often hide among stones. |
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What You'll Learn
- Caddisfly larvae are bioindicators of water pollution
- Larval forms of aquatic insects spend most of their lives underwater
- Dragonfly larvae are more sensitive to pollution than damselfly larvae
- Riffle beetle larvae are less sensitive to pollution than adults
- Larvae of benthic macroinvertebrates experience a range of seasonal conditions
Caddisfly larvae are bioindicators of water pollution
Caddisfly larvae are important bioindicators because they are large enough to be assessed conveniently in the field. They are also relatively easy to collect, as they can be found in most streams and rivers. Scientists often use a special net called a Surber Stream Bottom Sampler to collect caddisfly larvae and other invertebrates for analysis.
Caddisfly larvae are sensitive to a variety of pollutants, including urban and industrial wastewater discharges. They can be affected by increasing levels of metals such as iron, aluminium, zinc, copper, cobalt, nickel, lead, and cadmium. They are also impacted by changes in water quality, such as alterations in pH, temperature, and turbidity (water cloudiness).
The presence or absence of caddisfly larvae in a body of water can indicate the level of pollution. If caddisfly larvae are present, it suggests that the water quality is relatively good, as they cannot tolerate polluted waters. However, it's important to note that caddisfly larvae may have different tolerance levels to pollution depending on the species and environmental variables. Some species may be more tolerant of slight increases in pollutants, while others may be more sensitive to even small-scale pollution.
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Larval forms of aquatic insects spend most of their lives underwater
The larvae of aquatic insects have various methods of obtaining oxygen while underwater. Some carry a layer of air over their bodies and breathe using this air bubble until it is depleted, then return to the surface to replenish their air supply. Other types of insects have physical gills, which are combinations of hairs, scales, and undulations projecting from the cuticle, that hold a thin layer of air along the outer surface of the body. The volume of the film is small enough, and their respiration slow enough, that diffusion from the surrounding water is enough to replenish the oxygen in the pocket of air as fast as it is used. Insects of this type rarely need to return to the surface to replenish their air supply.
Aquatic insects have different ways of moving through the water. Some "climbers" move along the stems of vascular macrophytes or pieces of detritus. "Clingers" attach themselves to the surfaces of substrates exposed to water movement, such as rocks in streams. "Swimmers" periodically propel themselves through the water to change location, although they mostly remain attached to a substrate. "Divers" split their time between swimming to the surface, diving back through the water, and clinging to submerged objects. "Skaters" are adapted for life on top of the water surface, using hydrophobic body parts to move over the water. "Planktonic" forms float or swim about in open water.
The larval forms of aquatic insects are also sensitive to other environmental factors, such as salinity gradients. Most aquatic insects are salt-intolerant, but some, like brine flies, thrive in warm, saline water. Other chemical features, such as calcium concentration and total ionic strength, may also be important, but the specific requirements of different taxa are not yet well understood.
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Dragonfly larvae are more sensitive to pollution than damselfly larvae
Dragonflies and damselflies are part of the Odonata order of insects, spending their juvenile lives in the water and adulthood in the air and on land. Dragonflies and damselflies are both sensitive to pollution, but dragonflies are more negatively affected by urban contaminants than damselflies.
Dragonfly nymphs live in ponds or marshy areas where the water is calm, and some species burrow into soft substrates. Dragonfly larvae can be found in shallow areas of ponds, lakes, bogs, and wetlands, as well as in still portions of streams and rivers. Dragonfly nymphs are sensitive to pollution, especially those that wait burrowed in the sediment to ambush their prey. When nutrient pollution occurs, oxygen is first depleted, and dragonflies that are sensitive to low oxygen levels are impacted.
Damselfly nymphs, on the other hand, are mainly found in marshes, ponds, lakes, and streams. They crawl among submerged plants, rocks, and sediments at the bottom in search of prey. Damselflies are moderately tolerant of pollution and can be found in both still water and fast-running riffle areas of streams.
As cities expand, urban ecosystems can contribute to or hinder conservation efforts. While plant communities play a significant role in structuring dragonfly and damselfly communities, pond water quality is also important, especially for dragonflies. Chloride concentrations, for example, exceeded the guideline for protecting aquatic life in over two-thirds of the stormwater ponds in a study of ponds in Canada.
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Riffle beetle larvae are less sensitive to pollution than adults
Riffle beetles are aquatic beetles that live underwater in shallow, swift-flowing streams. They are sensitive to pollutants and environmental changes, and their presence or absence can indicate a stream's water quality. The adult riffle beetles are small, about the size of ants, and have oval-shaped bodies with long legs. They move slowly, crawling on submerged objects and remaining underwater.
The riffle beetle larvae, on the other hand, are elongated, multi-segmented, and rather hard and stiff, reaching about half an inch in length. They have 3 pairs of segmented legs near their heads, which are equipped with claws to enable them to cling to objects in turbulent water. The larvae walk on the bottom of streams and are not exposed to the water conditions for as long as the adults. This is the main reason why they are less sensitive to pollution than the adults.
Riffle beetles, in both their larval and adult forms, require plenty of dissolved oxygen in the surrounding water and are therefore mostly found in shallow, cool, flowing, and well-aerated streams. They feed on decaying vegetation, algae, and detritus, scraping the surfaces of submerged leaves, rocks, roots, and logs. The larvae build pupal chambers in the mud or sand along stream edges, and the pupation process lasts about two weeks.
Riffle beetles are an excellent indicator of water quality, especially in Missouri Ozark streams, which are typically rocky, clear, fast-flowing, and high-oxygen environments. Human threats to the survival of riffle beetles include reduced oxygen concentrations, elevated water temperatures, and pollution, especially from soaps and detergents.
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Larvae of benthic macroinvertebrates experience a range of seasonal conditions
Caddisfly larvae are another type of benthic macroinvertebrate larva that is sensitive to pollution. They are an indicator of good water quality and die out in polluted streams. Caddisflies are the most diverse insect order with exclusively aquatic members. They are useful as bioindicators because they are large enough to be assessed conveniently in the field.
Stoneflies are benthic macroinvertebrates that thrive in fast-flowing water with clean gravels. They are usually identifiable by their two tails and hairy-looking gills in their nymph stage. While they are environmentally sensitive, it is unclear how sensitive their larvae are to pollution.
Mayflies are another type of benthic macroinvertebrate larva that is used to indicate water quality. They are sensitive to pollution and cannot tolerate even small-scale exposure. However, it is unclear how sensitive their larvae are specifically.
Riffle beetle larvae are not as sensitive to pollution as the adults, mainly because they are not exposed to the water conditions for as long. They walk on the bottom of streams and are distinguishable from crane fly larvae, which look like large mosquitoes.
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Frequently asked questions
Fishfly larvae are sensitive to pollution. They are aquatic and spend most of their lives in the water, so they are easily affected by even small amounts of pollution.
The presence of fishfly larvae can be used as an indication of good water quality. If the water is polluted, the fishfly larvae will not be present.
Caddisfly larvae are also sensitive to pollution and are used as bioindicators of water quality. Other examples include mayflies, stoneflies, and dragonflies.
