Saskatchewan Aquatic Beetles (Coleoptera)

Acilius

The beetles as adults are easily identified by the elytra or harden shell-like forewings. The size can range from 2 mm to 3 cm depending on family and species. The larvae are much more variable in form. Some have large fang-like mandibles while others have chewing mouthparts. The legs can be reduced or well developed. The abdomen can have lateral projections on it or dorsal ornamentation. Size can vary as much as the size as the adult.

The largest order of insects is the Coleoptera with over 250,000 species. Only about 5000 species have aquatic stages. Even so the beetles are one of the most diverse freshwater macroinvertebrate groups. Eighteen families have species with at least one aquatic life stage. Only nine aquatic families occur in Saskatchewan. So far over 230 species of aquatic beetles have been reported or are likely to occur in Saskatchewan. About half belong to the family Dytiscidae.

The life cycle has four stages; egg, larva, pupa and adult. The number of stages that are aquatic varies among and within groups. However, with rare exceptions, the pupal stage is terrestrial.

Coleoptera are found in all types of aquatic habitats but the diversity is highest in lentic (standing) water. Evolutionary evidence suggests they invaded aquatic systems on many occasions. Each invasion resulted in different adaptations. This makes generalizations regarding ecology and life histories difficult. The Hydrophilidae have predatory larvae and the adults are omnivorous or herbivorous. Most Dytiscidae are predaceous in both stages. Predatory beetles either engulf their prey or grasp the prey with fang-like mandibles and inject digestive enzymes into the prey's body. The resulting "soup" is sucked out. Beetle larvae usually "breathe" through their integument (skin) or gills. Others use terminal spiracles that are protruded above the water surface. Adults carry an air bubble under the elytra or in hydrofuge body hairs that they must periodically return to the water surface to replenish.

Acilius

Special mention should be made of the Dytiscidae. This family is the largest aquatic beetle family in Saskatchewan. They inhabit all types of water bodies but due to their reliance on atmospheric oxygen are restricted to the shallow margins. Apparently, all species in the Saskatchewan have only one generation per year. Eggs are laid in spring by over wintering females and hatch soon after laying. The larval stage has three instars. Prior to pupation the final instar larvae crawl out of the water and dig a pupal chamber in litter along the shore. After a short pupation the adult emerges.

Another family of note is the Gyrinidae. This family is one of the most conspicuous and curious beetles found in Saskatchewan waters. Adults are usually seen in groups at the water surface swimming in a rapid and erratic manner. This behaviour gives them their common name of "whirligig beetle". The adult eyes are divided into upper and lower portions. This marvellous adaptation allows the beetles to live at the water surface and be able to see above and below without any distortion caused by the air/water interface.

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Below is a family key to the larvae and adults of common aquatic beetles found in Saskatchewan. Note that some uncommon larvae and adults are not keyed.

1a: Wings absent. Larvae.--2

1b: Elytra (hard fore wings) present. Adult beetles. Found in water or at times flying around lights.--Go to 7

2a: Legs made up of five segments. 3

2b: Larvae with only four segmented legs.--5

3a: Abdomen made up of nine or ten ~~~~~ segments--4

3b:Abdomen consisting of eight ~~~~~segments.--Dytiscidae

4a: Two claws at the end of each leg. Gill filaments~~~~~ present on abdominal segments. Four hooks at the end of the abdomen.--Gyrinidae (Note Berosus (Hydrophilidae) has lateral filaments but lacks four claws at the end of the abdomen and has four leg segments.)

4b: One claw at the end of the legs. Some have long spines on the top of the abdominal segments. Last abdominal segment formed into a long filamentA: Haliplus B: Peltodytes (note spines on segments)..--Haliplidae

5a: Eight abdominal segments. Most often the abdomen is soft~~~~~.--Hydrophilidae

5b: Body hard with nine abdominal segments.--6

6a: A ventral covering (operculum)Inset shows operculum on segment nine. on ninth abdominal segment. Found in flowing waters such as rivers and streams.--Elmidae

6b: No operculum on segment 9.--Hydrophilidae (In part)

Adult Beetles

7a: Each eye divided ~~~~ in two. Usually shiny black elytra. Often seen swimming on the water surface in groups.--Gyrinidae

7b: Eyes normal, not divided in two.--8

8a: Plates Arrow indicates plates. covering almost the entire first leg segment and first few abdominal segments.--Haliplidae

8b: No plates on ventral surface covering legs or abdominal segments.--9

9a: First segment of hind legs (coxae) dividing ~~~ the first abdominal segment. Overall body shape streamlined.--Dytiscidae

9b: First abdominal segment not divided ~~~ by hind coxae.--10

10a: Maxillary palps long, visible dorsally. Antennae with last four segments in the form of a club Arrow indicates club part of antenna. starting with a "cup-like" segment.--Hydrophilidae

10b: Maxillary palps short, not extending beyond head so no seen in dorsal view. Antennae may be clubbed or not Arrow indicates antenna. but not as above. Usually found in association with running water.--Elmidae

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Saskatchewan species list of aquatic beetles (Coleoptera):

(Please note if you do not have a "wheeled" mouse and a list expands below the page bottom just left click on the first entry of the list in question and use the keyboard's down arrow button to scroll down the list.)

References

Bousquet, Y.(ed) 1991. Checklist of Beetles of Canada and Alaska. Agriculture Canada.

Hooper, R. 2003. Pers. Comm.

Larson, D.J. 1987. Aquatic Coleoptera of peatlands and marshes in Canada. Mem. Ent. Soc. Can. 140:99-132

Larson, D.J., Y. Alarie and R.E. Roughley. 2000. Predaceous diving beetles (Coleoptera: Dytiscidae) of the Nearctic Region, with emphasis on the fauna of Canada and Alaska. NRC Res. Press, Ottawa, ON.

Mousseau, T. and R.E. Roughley. 2007. Taxonomy, classification, reconstructed phylogeny and biogeography of Nearctic species of Brychius Thomson (Coleoptera: Haliplidae). The Coleopterist's Bull. 61:351-397.

Smetana, A. 1988. Review of the family Hydrophilidae of Canada and Alaska (Coleoptera). Mem. Ent. Soc. Can. 142:1-316.

White, D.S. and R.E. Roughley. 2008. Chapter 20. Coleoptera. In. Merritt R.W. and K.W. Cummins. Ed. An Introduction to the Aquatic Insects of North America. 4th Edition. Kendall/Hunt Publishing Co. Dubuque, Iowa.