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Life in Freshwater

Feeding Relationships

Primary Production

Food Webs

Invertebrate Feeding methods

There are representatives of most of the different animal groups in both static and flowing water - some may just specialise more in one than the other. Hence we will deal with the way that invertebrates feed in one section.

Five main groups of feeders can be found and they are:

Feeding Category
Invertebrate Examples
Grazers & Scrapers Mayfly larvae, cased caddisfly larvae, pond snail, river limpet
Shredders Freshwater shrimp, the smaller stonefly larvae
Collector & Gatherers Chironomid midge larvae, worms, some mayflies (e.g. Ephemera
Collector & Filterers Black fly larvae and net-spinning caseless caddisfly larvae
Carnivores Dragonfly larvae, damselfly larvae, large stonefly larvae and alderfly Larvae

Photographic Examples:

Grazer

River Limpet
River Limpet: this shows the underside with the head down. A strap-like tongue (the radula) has teeth on it. This is protruded from the mouth by a muscle and then scraped along the rock surface. This pulls off periphyton (attached algae) and this is then ingested.

Collector - Filterer

Head of Mosquito Larva
Head of Mosquito Larva: The hairs at the end of the head are like a pair of brushes for sweeping up detritus and microscopic debris.


A caseless caddisfly larva
A caseless caddisfly larva out of water but within its web. This is spun to catch drifting material.

The cutting jaws of a caseless caddis
The cutting jaws of a caseless caddis

The short siphons of the Pearl Mussel
The short siphons of the Pearl Mussel. Water is drawn in and filtered of detritus.

Collector - Gatherer

Closeup of the head of a Chironomid larva
Closeup of the head of a Chironomid larva: the brush like fan of hairs is used to help collect detritus and bacteria. These larvae are extremely important in freshwater systems as a mid-stage link to larger animals - they help to convert detritus into food for fish and many predatory invertebrates.

 

Carnivore

The predators show amazing adaptations of parts of the head to secure the prey.

The labium of a damselfly larva
The labium of a damselfly larva. This "lower lip" is usually lying underneath the head but when it detects prey it is shot out under pressure at extreme speed. The hairy hooks on either side close round the prey and then brought back to the head where the mandibles eat the food, still held by the labium.

The head of a young Diving Beetle larva
The head of a young Diving Beetle larva. The jaws are narrow hypodermic needles for piercing the prey and drawing off the body fluids.

Head of the Phantom Midge
Head of the Phantom Midge. The dark blob is the compound eye for seeing the prey as it lies stationary in the water. The prey is grasped by a prehensile antenna held above the head. this brings it down against the second one and held in place so that the spikey mandibles can cut the prey up to swallow. The mandibles can be seen at the end of the yellowish gut.

 

 


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