102

CRAWLING WATER BEETLES

HALIPLIDAE

HALIPLIDAE—Crawling Water Beetles

family

Haliplidae

known species

220

distribution

Worldwide, but mostly found in the

Holarctic region

habitat

Slow-flowing or still water with algae.

Some species are found in fast-flowing

or even brackish water

size

2–4 mm

diet

Larvae primarily or entirely feed on algae.

Adults eat a wider variety of food, including

slow-moving, immobile, or dead invertebrates

T

he suborder Adephaga is divided into 11

families, of which nine are mainly or entirely

aquatic. One of the smaller aquatic families, which

is morphologically and ecologically quite distinct

from the others, is the crawling water beetle family

Haliplidae, which is widely distributed but usually

not particularly abundant, in still or slow-moving

fresh water throughout most of the world.

Haliplidae are called crawling water beetles

because they swim with a peculiar irregular stroke,

where each of the pairs of swimming legs alternate,

and they frequently climb over submerged

vegetation instead of swimming in open

water. The legs are not strongly adapted

for swimming, and have not developed

into paddles as in Dytiscidae or

Hygrobiidae. The adults of many

species disperse between water

bodies by flying during the night, and

are attracted to electric lights. Some

species, especially those living in large

lakes, tend to lose the ability to fly, but

like other Adephaga (notably Carabidae)

this may vary from population to

population, with the same species producing

flying and flightless individuals in response to

different ecological conditions.

below | Haliplus ruficollis feeding

on freshwater bryozoans in Europe.

Note the large air bubble held under

the coxal plates.