On this page you'll fine information and images of water beetles, meal worms, glow worms, and a stag beetle.

Water beetles

Nearly all water beetle adults are air breathing, so they have to rise to the surface for air which they often store under their elytra. Some rise tail first and others head first. Note the rear legs of all three beetles, they are fringed with hairs and bristles to aid in swimming, and are unsuitable for movement on land.

Above left is the whirligig beetle, in the family Gyrinidae, there are 12 species in Britain. True to its name, this is the beetle you will see gyrating around on the surface of the water. Its eyes are divided into two parts; the lower part is used for looking down and through water, and the upper for looking ahead and in the air, so it can see above and below the water sumultaneously. The most common whirligig in the UK is Gyrinus natator, and it should be a welcome resident in any garden pond as it feeds mainly on mosquito larvae. It can escape from danger below by flying and from above by diving into the water. It lays its eggs on submerged plants. The adults are 5 - 6 mm long. The larvae look like small centipedes(see the drawing below), and though highly predatory, tend to lurk in vegetation or detritus in shallow water. They have a small head, 3 pairs of legs, 1 pair of gills on each abdominal segmants except the last which has 4 hooks. They are predatory.

The beetle above left is a water beetle blonging to the Hydrophilidae family. Some of the species are wholly carnivorous, some vegetarian, and others omnivorous. They are much slower swimmers than the Dytiscidae (below). The way to tell the two families apart is to note the difference in sizes of their palps and antennae. In the Hydrophilidae the palps are longer, or at least as long as the antennae, and the antennae end in clubs. They collect thier air supply through their antennae, and it is stored as a bubble attched to the underside of the body. The larvae tend to be slow moving.

The beetle on the left is a male Dytiscus marginalis, the great water beetle, a member of the Dytiscidae family. There are 3 500 species world wide in this family, and 123 species in the UK. They range in length from 0.2 cm to 5.0 cm. Both larva (see below left) and adult are carnivorous, and the UK species have jaws powerful enough to puncture human skin.

All the adults in this family have the same oval-shaped body and fringed and flattened hind legs, which makes them powerful swimmers. Their air supply is carried under their hard fore wings (elytra). Usually the adults emerge in the late summer or early autumn. Pupation takes place out of the water. The larva digs a chamber in the bank. In the summer it can take just 2 or 3 weeks, but in the autum or winter the adult will not emerge until the spring.

Larva spend their time eating, adults stop eating only to mate.

Adult Dytiscus marginalis are dark brown/black with a greenish sheen and a yeallow margin. Although they are large, 27-35 mm in length, they are strong fliers. It is mainly the males that fly, and nearly always at night. They are searching for females. Unfortunately they often mistake greenhouses, shiny cars and even wet roads for water and crash land, sometimes with such violence that they die.
The females are similar to the males, but they do not have the wide front tarsi with suction pads. The male is very glossy, and the female less so. The female has longitudinal striations (grooves running lengthwise). They are found in weedy ponds, ditches and canals. Male Dytiscus marginalis have one large, nine medium and 160 small suckers on the undersides of their front pair of tarsi(see above). These help them hold on to the female while mating.

When I built my first pond we had a Dytiscus marginalis which we named Ghingis because it ate or attacked anything, even a human finger. Grabbing things with its front legs and pulling them towards its jaws. And it swam much faster than anything else in the pond. Then we found out she was a female, but the name stuck. And if we thought the adult was voracious that was nothing compared to the larvae, see left, which can reach 50 mm long. However I couldn't help liking Ghingis, and as we had a fairly large pond we just left her to eat knowing there were more than enough tadpoles for even her. However whatever you do do NOT have one of these in a small aquarium along with other animals, as pretty soon you will just have one hungry beetle.

The larva has hollow jaws/mandibles, and the juices of the prey are sucked up as if through a straw.

above an Indian stag beetle, Lucanus lunifer

The UK stag beetle, Lucanus cervus, flies at dusk in July making a whirring sound with its wings just before take off and landing.

Lucanidae Family
Stag beetle, Lucanus lunifer, left. This stag beetle is from India, but is very similar to the, now rare, British stage beetle, Lucanus cervus. There are around 1300 species of stag beetle worldwide. The adults are nocturnal and either do not feed, or feed only on fluids such as nectar. The males are always larger than the females, and have enlarged mandibles. They range in size from 0.6 - 8.5 cm. The Lucanidae larva (right) live in the root stock of deciduous trees especially oak, ash, beech elm and hawthorn, and can take 5 years to develop.