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Aquatic Macroinvertebrates
- 7% of the 91,000+ insects in North America are aquatic or semi-aquatic
- They are found in every type of waterway
Aquatic Insect Anatomy
- There are three main, distinct body regions that are common amongst aquatic insects.
- They are the head, thorax, and abdomen.
- Many aquatic insects, but not all, have a tail attached to the abdomen.
What is a macroinvertebrate?
- Macroinvertebrates are organisms without internal skeletons that can be seen with the unaided eye (often considered larger than 0.5 mm).
- The term aquatic macroinvertebrate can include
- arthropods – aquatic insects in all life cycle stages (nymphs, larva, pupa, or adults) and arthropods include crustaceans and aquatic arachnids.
- Mollusks
- Worms
- The first region, the head, is usually capsule-like and contains the sensory organs, differing mouthparts, and often compound eyes.
- Antennae and mouthparts are sometimes used as identification characteristics for aquatic bugs.
Head
Thorax
- The second region is the thorax, often subdivided into the prothorax, mesothorax, and metathorax.
- An insect’s legs (3 pair) will be found on the thorax.
- Sometimes wing pads can be seen, showing where the adult’s wings will one day develop.
Abdomen
- The abdomen is usually the longest body region composed of several segments.
- Sometimes the number of segments is an identification characteristic.
- There might be some appendages attached to the abdomen, but they are not legs.
- They can be
- prolegs (fake legs),
- filaments,
- gills,
- breathing tubes,
- hairs, and bristles – all serving specific functions for the insect.
- A variety of tails sometimes called cerci can extend from the abdomen.
- All these appendages and tails can also be identification
characteristics.
Aquatic Insect Anatomy - Breathing
Aeropeustic - "Air Breathing"
- Find a way to get oxygen from the atmosphere even though they live in the water
Snorkel Approach
- remaining just below the surface and sticking a breathing tube above.
Scuba Approach
- While underwater, they carry an oxygen rich air bubble on the underside of their body.
- Another minor group of insects can pierce into the stems of aquatic plants to obtain oxygen inside
- Able to survive in low dissolved oxygen settings
- Low oxygen can be a sign of pollution
Hydroneustic-"Water Breathing"
- Breathing through Gills
- Need sufficient DO levels to survive
Aquatic Insects Life Cycles
- The majority of aquatic macroinvertebrates that inhibit waterways are simply the juvenile form of an adult, land-dwelling insect.
- Many aquatic insects start off life underwater.
- Because their immature aquatic bodies are specially suited for life underwater, they often do not resemble their land-dwelling, adult body form.
- Before the juvenile aquatic insect can leave its original aquatic home, it must undergo several physical changes to prepare itself for life on land. This change in physical appearance is called metamorphosis.
Types of Metamorphosis
- The extent of change that the aquatic organism undergoes varies from organism to organism.
- There are two types of metamorphosis complete metamorphosis and incomplete metamorphosis.
- Almost 90% of the insects that undergo metamorphosis undergo complete metamorphosis.
- Complete metamorphosis consists of four stages. The organism begins as an egg, then is hatched a larva, (often resembles little of mature adult), which gradually matures into a pupa, which then wraps itself into a cocoon, where it finally transforms into the adult land-dwelling insect.
Complete Metamorphosis
Complete metamorphosis consists of four stages.
1. The organism begins as an egg
2. then is hatched a larva (often resembles little of mature adult),
3. which gradually matures into a pupa,
4. which then wraps itself into a cocoon, where it finally transforms into the adult land-dwelling insect.
Incomplete Metamorphosis
- Incomplete metamorphosis has only three main stages of development.
1. The insect again begins as an egg,
2. which is hatched and becomes a nymph.
3. Nymphs are a miniature version of the adult form.
- They are sexually immature, and grow larger through a series of molts until they reach full size and develop wings. This is the adult stage.
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