The Crustaceans & Arachnida


Art by: C. Ruth Neudahl
Text by: Valerie Brady

Note the size of the real penny and use it to judge the size of the bugs in the following pictures.


Phylum: Arthropoda, the arthropods

Class: Crustacea, the crustaceans

Order: Amphipoda, scuds and sideswimmers

Size: 0.2-0.8 inch (5-20 mm)

Habitat & Habits: Amphipods are laterally (side-to-side) flattened, and so appear to be lying on their sides much of the time. These fast, darting swimmers are common in lakes and ponds, and are sometimes found in streams. Most often, scuds are associated with detritus, debris, and soft sediments. They are important fish food, and several tied flies imitate them.

Feeding: Most amphipods are particle collectors and detritus shredders (i.e. scavengers).

Water Quality Indicator: Amphipods are moderately intolerant to very tolerant of nutrient pollution, depending on species.

Class: Crustacea, the crustaceans

Order: Decopoda, crayfish and shrimp

Family: Astacidae, crayfish

Size: Up to 6 inches (150 mm)

Habitat & Habits: Crayfish are found in many shallow freshwater habitats, usually in burrows or under rocks or debris. They can scoot backwards rapidly to escape capture.

Feeding: Some species are predators, others are scavengers, and still others feed on algae

Water Quality Indicator: Crayfish are not typically used as water quality indicators.


Phylum: Arthropoda, the arthropods ("Ajoined Appendages")

Class: Arachnida - spiders, mites, and scorpians

Order: Acari - ticks and mites

Suborder: Hydracarina, aquatic mites

Size: Less than 0.2 inch (4 mm)

Habitat & Habits:Aquatic mites are typically seen as small dots or ovals swimming energetically through the water; some species resemble ticks. These often brightly-colored animals are found swimming or crawling through the substrate in most freshwater habitats. Some species attach to aquatic invertebrates

Feeding: Young mites are primarily parasitic on aquatic or terrestrial invertebrates; adult mites are predators on small invertebrates or eat detritus.

Water Quality Indicator: Unknown