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Aquatic Insects. 8 April 2009. Aquatic Insects. Insecta (even Hexapoda) are plesiomorphically terrestrial . But there have been numerous colonizations of the freshwater aquatic environment. Far fewer colonizations of marine aquatic environment. Hemimetabolous Aquatic Insects.

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Aquatic insects

Aquatic Insects

8 April 2009

Aquatic insects1
Aquatic Insects

  • Insecta (even Hexapoda) are plesiomorphically terrestrial.

  • But there have been numerous colonizations of the freshwater aquatic environment.

  • Far fewer colonizations of marine aquatic environment.

Hemimetabolous aquatic insects
Hemimetabolous Aquatic Insects

  • Some lineages have almost* exclusively aquatic naiads.

    • Ephemeroptera

    • Odonata*

    • Plecoptera (the only aquatic Polyneoptera)

  • All of these have terrestrial adults.

Hemimetabolous aquatic insects1
Hemimetabolous Aquatic Insects

  • There are multiple colonizations of aquatic environments by Heteroptera.

  • Most of these are also aquatic as adults.

Holometabolous aquatic insects
Holometabolous Aquatic Insects

  • Colonized aquatic environments much more recently.

  • Numerous colonizations within numerous orders

  • Only two have exclusively* aquatic larvae.

  • Only some Coleoptera remain aquatic as adults.

Holometabolous aquatic insects1
Holometabolous Aquatic Insects

  • Neuroptera: One lineage (Sisyridae, spongillaflies).

  • Coleoptera: Numerous colonizations throughout.

  • Diptera: Numerous colonizations, especially in Nematocera.

  • Lepidoptera: Numerous origins, but NOT common

Habitats for aquatic insects
Habitats for aquatic insects

  • Lotic: flowing water

    • Influenced strongly by velocity of flow

      • Particle size

      • Substrate type

    • Inputs from outside and local nutrient supplies

  • Lentic: standing water

    • Often strong zonation

      • Limnetic zone- penetrated by light

      • Profundal zone- deeper zone w/o much light

Unusual habitats
Unusual Habitats

  • Marine environments

    • Intertidal habitats

      • Between high and low tide

      • biting flies, plant feeding insects, detritivores

    • Littoral habitats

      • Coastal regions with shallow water

      • Some midges and beetles

    • Open ocean: water striders feeding on food of terrestrial origin

  • RARE! WHY???

Unusual habitats1
Unusual Habitats

  • Temporal water bodies (e.g. vernal pools)

    • Common in areas with seasonal rainfalls

  • Numerous adaptations

    • Ability to find ephemeral pools (meteorological cues?)

    • Desiccation resistant diapause

      • Very common as eggs

      • Some with ability to undergo numerous dehydrate/rehydrate cycles: anhydrobiosis

  • Plant container habitats: Phytotelmata

Oxygen supplies
Oxygen Supplies

  • Air: 200,000 ppm (20%)

  • Lotic environments (15 ppm)

    • Depends on O2 production/consumption by plants

    • Affected by turbulence and water quality

  • Lentic environments

    • Oxygen levels vary with temperature, salinity, and depth

    • Turbulence affects nutrient and oxygen distribution

  • Anoxic

    • No oxygen present

How do aquatic insects obtain oxygen
How do aquatic insects obtain oxygen?

  • Atmospheric oxygen

    • Keep part of body out of water

    • Carry oxygen into water

  • Aqueous oxygen

    • Use of open tracheal system

      • Adult insects

      • Immature forms

    • Use of closed tracheal system

      • Specialized structures for gas exchange in water

      • Often adults have open tracheal system

Closed tracheal system
Closed Tracheal System

  • Gills- lamellar extensions of tracheal system

  • Found in many insect orders

  • Gills may be in many places

    • Base of legs

    • Abdomen

    • End of abdomen

    • How is this analogous to insect ears?

Open tracheal system in flies
Open tracheal system in flies

  • Respiratory siphons near abdomen or thorax

  • Different location in mosquito pupa than larva

Open tracheal system in diving beetles
Open tracheal system in diving beetles

  • Bubble stored beneath elytra

  • Gas exchange can occur in water

Does the bubble increase linearly with oxygen consumption?

What happens to the exhalation product?

Other air bubble gills
Other air bubble gills

  • Water kept away from body through ‘hairs’ or ‘mesh’

  • Oxygen diffuses from water to air against body

  • Usually slow moving insects with low oxygen demand

Lotic adaptations
Lotic Adaptations

  • Flattened bodies

  • Attachment through suckers

Water pennies (Coleoptera: Psephenidae)

Net-winged midges

(Diptera: Blephariceridae

More lotic adaptations
More Lotic Adaptations

  • Nets & Cases

Trichoptera net

Trichoptera cases

Lentic adaptations
Lentic Adaptations

Water Strider (Gerridae)

  • Taking advantage of surface tension of still water

Whirligig Beetle (Gyrinidae)

Adaptations to nearly anoxic environments
Adaptations to nearly anoxic environments

  • Hemoglobins

    • Many larval chironomid midges (Diptera) = bloodworms

    • Some notonectid bugs (Heteroptera) = backswimmers

    • Very, very high affinity for oxygen (unlike us)

    • Only downloads when oxygen concentrations in tissues decrease, not when tissues become acidic

Using insects to monitor aquatic environments
Using insects to monitor aquatic environments

  • Usefulness

    • Diverse taxa to choose from, many common

    • Functionally important to ecological community

    • Ease of sampling many individuals without major ethical constraints

    • Ability to identify species

  • Responses

    • Increases of certain taxa in waters with sediment, low

    • Oxygen, increases in temperature

    • Loss of diversity with pollution and or eutrophication


  • Naiads often with abdominal gills

    • Also maxillary and labial gills!

  • Generally 3 styli on naiads and adults.

  • As many as 45 instars

  • Anything else?


  • Dragonflies & Damselflies

  • Rectal/anal internal gills.

  • Caudal lamellae also serve as gills.

  • Up to 20 instars.

  • Predators as naiads and adults.


  • Mostly temperate regions

  • 10-33 instars

  • Closed tracheal system with anal gills.

  • Need high oxygen, good environmental indicators.

Hemiptera true bugs
Hemiptera: True Bugs



  • Diving or at surface

  • Adults and naiads both aquatic.

  • Highly modified legs.

  • Generally wings still functional as adults, can disperse between waterways.


Water Boatmen


Creeping water bugs


Water striders


  • Left: Nepidae (water scorpions) tails are breathing tubes

  • Right: Belostomatidae (toe-biters) egg tending by males


  • Case & net makers.

  • Abdominal tracheal gills.


  • Aquatic larvae, aquatic adults

  • Aquatic larvae, terrestrial adults

  • Terrestrial larvae, aquatic adults

  • Pretty much all pupate on land


  • Often with anal spiracles breathing at surface

  • Very diverse

  • Almost all disease vectoring Diptera have aquatic larvae (?)