Common Aquatic Insects of Freshwater Ecosystems

Contribution and Photo credits
Dr. Rabindra Hazarika
Assistant Professor, Department of Zoology
Darrang College, Tezpur, Assam 

Aquatic insects occupy every kind of freshwater habitat including temporary streams and ponds, the shallowest and deepest areas of lakes, the most pristine and polluted rivers, roadside ditches, within and on macrophytes and susceptible to all ranges of water chemistry from acidified to alkaline bodies of water. They also represent all the functional feeding groups including predators, shredders, grazers (or scrapers), filter feeders, gatherers, piercers and parasites (Mackie, 2001). A study on aquatic insect fauna is one of the important aspects of freshwater biology.  Aquatic insects form an important link in many food chains. They consume other invertebrates, small fish, aquatic plants, algae, detritus and decaying matter. Aquatic insects are also an important food source for birds, fishes, reptiles and amphibians. They have a trophic link with terrestrial consumers like insectivorous birds (Danforth, 1926), which give them a higher consideration for the management of the wetland as a wildlife refuge. For example, water birds select high protein insects over low protein plant food during the breeding season due to the increasing demands of egg-laying and gonads development (Murkin and Wrubleski, 1988).

             1. Micronecta scuttellaris scuttellaris

Diagnostic characters: It is the largest species of the genus (2.8 to 3.1mm). Pronotum greyish or greyish brown, paler margin with obscure elytral pattern; the tip of the left paramere club-shaped and possesses minute denticles.

Distribution in India:  Andhra Pradesh, Assam, Bihar, Chandigarh, Delhi, Gujarat, Himachal Pradesh, Karnataka, Kerala, Madhya Pradesh, Maharashtra, Manipur, Orissa, Punjab, Rajasthan, Tamilnadu, Uttar Pradesh, West Bengal.

Remarks:  The species of water boatman is very widely distributed in India and mostly found in stagnant pools, ponds and ditches. An exceedingly light attracted insect abundantly recorded from the studied ponds throughout the year. It can be best collected using a light trap.

                                                             2. Nychia marshalli

Diagnostic characters: Males are little longer than females, attain a length of 5.2mm while female reach up to 4.8mm approximately; head with vertax a little raised; eyes holopneustic, the postero-lateral margin of eyes E-shaped; pronotum short and transverse with concave anterior angles; hemelytra without any claves; posterior legs slender and longer than the body length; hemelytra fully cover the body in the females while in males last three abdominal segments remain uncovered.

Distribution in India: Assam, Pondicherry; Tamilnadu; West Bengal.

Remarks: They are powerful swimmer but for a short distance and swim by means of rapid strokes with the help of the last pair of legs.

                                                               3. Plea liturata

Diagnostic characters: A small insect, body about 2mm long, dull yellowish-grey in colour; front of the head provided with markings; pronotum with fine punctures spread all over; abdominal keels prominent and not compact.

                  Distribution in India: Assam, Bihar, Delhi, Madhya Pradesh, Tripura, West Bengal.

Remarks: Plea liturata belonging to the Pleidae are small insects that are usually less than 3mm and commonly known as ‘pigmy back-swimmer’. They are short-legged bugs, anterior leg modified for grasping.  Head is relatively large, antennae short. 

                            4. Laccotrephes griseus

Diagnostic Characters: Abdomen above with light bluish tinge; anterior area of prosternum provided with a strong acute spine-like structure; abdominal appendages distinctly shorter than the body; the parameres are symmetrical and slightly hooked.

Distribution in India: Andhra Pradesh, Arunachal Pradesh, Assam, Bihar, Chandigarh, Delhi, Gujarat, Himachal Pradesh, Karnataka, Kerala, Madhya Pradesh, Maharashtra, Manipur, Meghalaya, Nagaland, Orissa, Pondicherry, Rajasthan, Tamilnadu, Tripura, Uttar Pradesh, West Bengal.

Remarks: Laccotrephes griseus commonly also known as Nepa belonging to the family Nepidae includes the insects commonly known as the water scorpions because the forelegs of these insects somewhat resemble the pedipalps of a scorpion. They have long siphon at the end of their abdomen. The water scorpion is very common in peninsular India.

5.  Ranatra filiformis

Diagnostic character: Adult attains a length of about 27-28mm and abdominal appendages about 23mm; both the teeth on anterior femur spinulose; head may be provided with distinct tubercle on the vertax.

Distribution: Andhra Pradesh, Arunachal Pradesh, Assam, Bihar, Chandigarh, Delhi, Gujarat, Himachal Pradesh, Karnataka, Kerala, Madhya Pradesh, Maharashtra, Manipur, Meghalaya, Orissa, Pondicherry, Rajasthan, Tamilnadu, Tripura, Uttar Pradesh, West Bengal.

Remarks: The species is mostly found among the submerged part of vegetation. Found mainly in association with aquatic vegetation especially with Eichhornia crassipes.

6. Diplonychus rusticus

Diagnostic characters: Lateral basal margin of pronotum and embolium pale; tarsi 1-jointed and with a smaller claw; suboval in shape.

Distribution in India: Andaman & Nicobar Island, Assam, Andhra Pradesh, Arunachal Pradesh, Bihar, Chandigarh, Delhi, Goa, Gujarat, Himachal Pradesh, Jammu and Kasmir, Karnataka, Kerala, Madhya Pradesh, Maharashtra, Manipur, Meghalaya, Orissa, Pondicherry, Punjab, Rajasthan, Tamilnadu, Tripura, Uttar Pradesh, West Bengal.

Remarks: The water bug is a common inhabitant of stagnant water bodies; voracious feeder and attack fish fry and fingerling; the species shows parental care, male carries the eggs deposited by the female on the back.

7. Lethocerus indicus

Diagnostic Characters: Large size insect (62-85mm). Head between eyes with parallel sides; pronotum with a transverse fasciae at the basal end and a fine longitudinal carination in the middle; thick sets of swimming hairs on intermediate and posterior legs on the ventral side.

Distribution in India: Andaman and Nicobar Islands, Andhra Pradesh, Arunachal Pradesh, Assam, Bihar, Chandigarh, Delhi, Goa, Gujarat, Himachal Pradesh, Jammu and Kashmir, Karnataka, Kerala, Madhya Pradesh, Maharashtra, Manipur, Meghalaya, Mizoram, Orissa, Pondicherry; Punjab, Rajasthan, Tamilnadu, Tripura, Uttar Pradesh, West Bengal.

Remarks:  Lethocerus indicus commonly known as Belostoma belonging to the largest species of aquatic Hemipterans is a voracious feeder of fry and fingerlings of fishes and has been reported to kill even a full-grown frog while some are reported to feed on the snail.

8.   Mesovelia vittigera

Diagnostic characters: Adults attain a length about 2.5-3.0mm; body elongated with a prominent head; antennae 4-jointed, 2^nd joint shortest; eyes large almost touching the anterior margin of pronotum

Distribution in India: Assam, Arunachal Pradesh, Andaman & Nicobar Islands, Bihar, Karnataka, Kerala, Maharashtra, Orissa, Pondicherry, Tamilnadu, Uttar Pradesh, West Bengal.

Remark: The semi-aquatic bug is very common in ponds, found among the floating vegetation runs very fast on the water surface.

9. Hydrometra greeni

Diagnostic characters: Body elongate about 11-12mm long, head very long, longer than pronotum, eyes far from anterior margin of pronotum, antennae 4-jointed, 1^st segment very short, 2^nd and 4^th subequal, 3^rd segment longest, hemi-elytra shorter than the abdomen.

Distribution in India: Assam, Arunachal Pradesh, Andaman & Nicobar Islands, Bihar, Gujarat, Karnataka, Kerala, Maharashtra, Orissa, Pondicherry, Rajasthan, Tamilnadu, Uttar Pradesh, West Bengal.

Remark: The species is found on the surface of water among the vegetation. The semi-aquatic insect is widely distributed in India. They are extremely slender insects, with a stick-like body and thread like-legs. Head elongated, as long as thorax, eyes large, placed slightly behind the middle of the head. They are found near the surface film.

10. Neogerris parvula

Diagnostic characters: The body length of adult insect is 6-6.5mm; 1^st segment of antennae is longest and as long as the 2^nd and 3^rd segments together; 4^th segment is nearly half in length than the 1^st segment; anterior part of pronotum with a single roundish yellow patch.

Distribution in India: Assam, Arunachal Pradesh, Kerala, Orissa, Pondicherry, Tamilnadu, Uttar Pradesh, West Bengal.

Remarks: It is one of the common semi-aquatic hemipteran species. The semiaquatic long-legged Hemipterans are commonly known as ‘Water striders’ or ‘Pond skaters’ as they are found skating or leaping about on the surface film of ponds. They are gregarious in nature and occur in large blackish masses. When disturbed, they scatter in all directions.