Enochrus quadripunctatus - microcosmos.nl

Enochrus quadripunctatus clambers among decaying plants.

Ten species of Enochrus occur in the Netherlands, the most common being Enochrus testaceus (Nieukerken, 1992). The depicted Quadripuncatus species is named after the four black dots surrounding a larger, round black spot on the pronotum. In this specimen, the two front dots are connected by a line. The species is not common everywhere. I found it in the same shallow pool as the Colymbetes fuscus specimen on this site. This handsome, approximately 5-millimeter-long Enochrus beetle clambers slowly through aquatic plants and decaying remains, where it may find algae and other small matter as food. Underwater, the real antennae are folded under the head; the 'antennae' we see on the left are the maxillary palps.

An air bubble is held on the belly. This is refreshed by pushing one of the club-shaped antennae against the water surface, creating a small air channel to the air on the belly.

In this species, the 2nd segment of the maxillary palp is curved and yellow. The 4th segment is shorter than the 3rd and has a black tip. Move the mouse pointer over the left image to see an indication of the four spots.

The little beetle can walk upright, but due to the large air bubble, it often hangs upside down. Without a foothold, it shoots up like a cork and then dangles quite helplessly just below the surface. That is why it is truly in its element among plants and algae.

These beetles on the right were apparently mating when they were caught; the male had slid off the female (perhaps due to the disturbance with the net), and so they were stuck together for hours. Unfortunate, but eventually they managed to get free.

As a true member of the spinning water beetle family, Enochrus wraps the eggs in a silken cocoon. This egg nest is about 2 mm in size and is equipped with a thin ribbon, 4 to 8 mm long. The eggs hatch in July. ¹)

THE LARVA

Enochrus larvae resemble small, grey caterpillars with a flat head. Like butterfly caterpillars, they have wart-like projections on their abdomen. The six true legs are small. They live in very shallow water and sit constantly half submerged and half above the water. The tip of the tail is constantly touching the water surface for contact with the outside air. They catch ostracods, which they hold above water to digest the prey with their saliva, which contains dissolving enzymes.

The larvae pupate after a few weeks into beetles in air bubbles within floating patches of filamentous algae, so in the water and not, as is the case with most water beetles, on land. ¹)

¹) According to: Wesenberg Lund, "Das leben der Süßwasserinsekten" (1943)

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