- Microcosmos.nl -
Rhantus suturalis, slant top view 24-07-2007
enlarge Rhantus suturalis
THIS BEETLE IS WORLDWIDE VERY COMMON IN LITTLE POOLS THAT DRY OUT DURING SUMMER.
rhantus suturalis with air bubble 24-07-2007
Rhantus suturalis enlarge
with air bubble
Those pools are also the breeding places of mosquito larvae - the preferred food of this beetle. As the beetle also often visits garden pools, that means less mosquito bites for us! The specimen of these photos had landed in a fish tank that was standing in my garden. And it must have laid a few eggs there, because some days later suddenly I saw it's little larvae.
The beetles of the genus Rhantus are medium sized, apparently dark brown beetles which are, like all diving beetles, excellent swimmers. They can also fly very well, and so easily escape from a pool which is drying out and migrate to another. With a closer look at Rhantus suturalis the dense black punctuation of the elytra is visible, this punctuation on a golden yellow base gives the dark brown impression when seen from a normal distance. Older names (synonyms) for this beetle reflect this punctuation: Rhantus pulverosus and Rhantus punctatus. The beetle has a light yellow coloured margin. Just like all members of the diving beetles family (Dytiscidae) this beetle keeps a supply of air under its elytra, that is refreshed by protruding the tip of the abdomen above the water surface. When under water the insect now and then presses the air from under the elytra into a relatively large air bubble, that is held at the tip of the abdomen. By diffusion oxygen in the water will migrate in this bubble. After some time the beetle sucks the refreshed air bubble back in by enlarging the space between its abdomen and elytra. In this manner the air supply is longer usable, and the bubble is what is called a physical gill. The beetle shows this behaviour more when it wants to hide and remain longer under water. Sometimes the bubble is the only thing that is revealed of the hidden insect.

Rhantus suturalis, at the water surface 24-07-2007.
enlarge Rhantus suturalis aspirating
Rhantus exsoletus 24-06-1999
enlarge Rhantus exsoletus
Small pools with mosquito larvae can be found almost at any place on the world, and the same goes for the beetles of the Rhantus genus. There are a number of species in Europe, a few are very common. Rhantus suturalis, a worldwide spread species, is recognisable by a rhombus-shaped dot on the neck shield. At the right: Rhantus exsoletus, another very common species that has a vague-black margin at the end of the neck shield instead of a rhombus-shaped dot. At the under side this beetle is not totally black like suturalis, but yellow. Please notice the (not specific) differences in the spots on the heads.

Rhantus suturalis 08-09-2007 Rhantus exsoletus 24-06-1999
On the pictures at right the two species are presented. (R. suturalis is resting horizontally on the bottom, while R. exsoletus sits vertically on a leaf.) In a superficial glance the beetles look the same. It's a pity the position of the heads is different on the two pictures, this makes comparison more difficult. As is shown on the picture under, R. suturalis has a black under side where R. exsoletus is more yellow.
Rhantus suturalis 24-07-2007


NEXT PAGE: THE LARVA



terug
back to: WATERBEETLES 1

Page track: INDEX » diving beetles » Rhantus suturalis

COPYRIGHT:
All pictures on this site were made by Gerard Visser (Almelo, Netherlands), unless stated otherwise. All rights remain with him. These pictures may not be used for purposes any other than private viewing or printing. Do NOT hardlink to these pictures or place them on other websites without the author's approval. Should you need them for purposes which include third parties, you must ask the author permission by e-mail. People, who want to use this pictures for exhibitions or publications or educative material are much encouraged to do so, after approval as mentioned and giving the normal credits.
© G.H. Visser 24-08-2007
rev. 27-10-2007


Deze pagina in het Nederlands dutch Dutch page

http://www.microcosmos.nl/beet1/rhantus.htm

Valid XHTML 1.0!

terug naar beetles 1
beetles 1